[Sony Xperia X Compact Themes, Apps, and Mods] SXUsr:
[IMG="X Compact 4 button navbar"]http://i63.tinypic.com/6zocpg.png[/IMG]​

1. Decompile your SytemUI.apk

2. Navigate to res/layout/navigation_bar.xml and copy the whole code below and replace it with yours...

<?xml version="1.0" encoding="utf-8"?>
<com.android.systemui.statusbar.phone.NavigationBarView android:background="@drawable/system_bar_background" android:layout_width="fill_parent" android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:systemui="http://schemas.android.com/apk/res-auto">
<FrameLayout android:id="@id/rot0" android:layout_width="fill_parent" android:layout_height="fill_parent">
<LinearLayout android:orientation="horizontal" android:id="@id/nav_buttons" android:clipChildren="false" android:clipToPadding="false" android:layout_width="fill_parent" android:layout_height="fill_parent" android:animateLayoutChanges="true">
<View android:visibility="invisible" android:layout_width="@dimen/navigation_side_padding" android:layout_height="fill_parent" android:layout_weight="0.0" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/back" android:layout_width="70.0dip" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_back" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_back" systemui:keyCode="4" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/home" android:layout_width="70.0dip" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_home" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_home" systemui:keyCode="3" systemui:keyRepeat="false" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/recent_apps" android:layout_width="70.0dip" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_recent" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_recent" systemui:keyCode="187" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/newmenu" android:layout_width="70.0dip" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_menu" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
<View android:visibility="invisible" android:layout_width="70.0dip" android:layout_height="fill_parent" android:layout_weight="0.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/menu" android:visibility="invisible" android:layout_width="@dimen/navigation_extra_key_width" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_menu" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
<FrameLayout android:layout_width="@dimen/navigation_extra_key_width" android:layout_height="fill_parent" android:layout_weight="0.0">
<com.android.systemui.statusbar.policy.KeyButtonView android:layout_gravity="end" android:id="@id/menu" android:visibility="invisible" android:layout_width="@dimen/navigation_extra_key_width" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_menu" android:scaleType="centerInside" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
<com.android.systemui.statusbar.policy.KeyButtonView android:layout_gravity="end" android:id="@id/ime_switcher" android:visibility="invisible" android:layout_width="@dimen/navigation_extra_key_width" android:layout_height="fill_parent" android:src="@drawable/ic_ime_switcher_default" android:scaleType="centerInside" android:contentDescription="@string/accessibility_ime_switch_button" />
</FrameLayout>
</LinearLayout>
</FrameLayout>
<FrameLayout android:id="@id/rot90" android:paddingTop="0.0dip" android:visibility="gone" android:layout_width="fill_parent" android:layout_height="fill_parent">
<LinearLayout android:orientation="vertical" android:id="@id/nav_buttons" android:clipChildren="false" android:clipToPadding="false" android:layout_width="fill_parent" android:layout_height="fill_parent" android:animateLayoutChanges="true">
<FrameLayout android:layout_width="fill_parent" android:layout_height="@dimen/navigation_side_padding" android:layout_weight="0.0">
<com.android.systemui.statusbar.policy.KeyButtonView android:layout_gravity="top" android:id="@id/ime_switcher" android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="@dimen/navigation_extra_key_width" android:src="@drawable/ic_ime_switcher_default" android:scaleType="centerInside" android:contentDescription="@string/accessibility_ime_switch_button" />
<com.android.systemui.statusbar.policy.KeyButtonView android:layout_gravity="top" android:id="@id/menu" android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="40.0dip" android:src="@drawable/ic_sysbar_menu" android:scaleType="centerInside" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
</FrameLayout>
<View android:visibility="invisible" android:layout_width="0.0dip" android:layout_height="fill_parent" android:layout_weight="1.0" />
<View android:visibility="invisible" android:layout_width="0.0dip" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/newmenu" android:layout_width="fill_parent" android:layout_height="70.0dip" android:src="@drawable/ic_sysbar_menu" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/recent_apps" android:layout_width="fill_parent" android:layout_height="70.0dip" android:src="@drawable/ic_sysbar_recent" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_recent" systemui:keyCode="187" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/home" android:layout_width="fill_parent" android:layout_height="70.0dip" android:src="@drawable/ic_sysbar_home" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_home" systemui:keyCode="3" systemui:keyRepeat="false" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/back" android:layout_width="fill_parent" android:layout_height="70.0dip" android:src="@drawable/ic_sysbar_back" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_back" systemui:keyCode="4" />
<View android:visibility="invisible" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.systemui.statusbar.policy.KeyButtonView android:id="@id/menu" android:visibility="invisible" android:layout_width="70.0dip" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_menu" android:scaleType="center" android:layout_weight="0.0" android:contentDescription="@string/accessibility_menu" systemui:keyCode="82" />
</LinearLayout>
</FrameLayout>
<com.android.systemui.statusbar.phone.NavigationBarInflaterView android:id="@id/navigation_inflater" android:layout_width="fill_parent" android:layout_height="fill_parent" />
</com.android.systemui.statusbar.phone.NavigationBarView>

3. Navigate to res/values/ids.xml and add the following code to the bottom...

<item type="id" name="newmenu">false</item>

...recompile your SystemUI.apk, install it, reboot, done.

The stock 3 button softkey image will display after doing this, the images I'm using came from this thread - [SOFTKEYS] Softkey Collection so a big thanks to [MENTION=2539590]atticus182[/MENTION] for them.