[Nexus 6 Themes and Apps] coolexe:
yes easy.

stock status_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<com.android.systemui.statusbar.phone.PhoneStatusBarView android:orientation="vertical" android:id="@id/status_bar" android:background="@drawable/system_bar_background" android:focusable="false" android:descendantFocusability="afterDescendants"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:systemui="http://schemas.android.com/apk/res/com.android.systemui">
<ImageView android:id="@id/notification_lights_out" android:paddingBottom="2.0dip" android:visibility="gone" android:layout_width="@dimen/status_bar_icon_size" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_lights_out_dot_small" android:scaleType="center" android:paddingStart="6.0dip" />
<LinearLayout android:orientation="horizontal" android:id="@id/status_bar_contents" android:layout_width="fill_parent" android:layout_height="fill_parent" android:paddingStart="6.0dip" android:paddingEnd="8.0dip">
<com.android.systemui.statusbar.AlphaOptimizedFrameLayout android:orientation="horizontal" android:id="@id/notification_icon_area" android:layout_width="0.0dip" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.keyguard.AlphaOptimizedLinearLayout android:orientation="horizontal" android:id="@id/system_icon_area" android:layout_width="wrap_content" android:layout_height="fill_parent">
<include layout="@layout/system_icons" />
<com.android.systemui.statusbar.policy.Clock android:textAppearance="@style/TextAppearance.StatusBar.Clock" android:gravity="start|center" android:id="@id/clock" android:layout_width="wrap_content" android:layout_height="fill_parent" android:singleLine="true" android:paddingStart="@dimen/status_bar_clock_starting_padding" android:paddingEnd="@dimen/status_bar_clock_end_padding" />
</com.android.keyguard.AlphaOptimizedLinearLayout>
</LinearLayout>
<ViewStub android:id="@id/emergency_cryptkeeper_text" android:layout="@layout/emergency_cryptkeeper_text" android:layout_width="wrap_content" android:layout_height="fill_parent" />
</com.android.systemui.statusbar.phone.PhoneStatusBarView>

for center clock

<?xml version="1.0" encoding="utf-8"?>
<com.android.systemui.statusbar.phone.PhoneStatusBarView android:orientation="vertical" android:id="@id/status_bar" android:background="@drawable/system_bar_background" android:focusable="false" android:descendantFocusability="afterDescendants"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:systemui="http://schemas.android.com/apk/res/com.android.systemui">
<com.android.systemui.statusbar.policy.Clock android:textAppearance="@style/TextAppearance.StatusBar.Clock" android:gravity="start|center" android:id="@id/clock" android:visibility="gone" android:layout_width="0.0dip" android:layout_height="0.0dip" android:singleLine="true" android:paddingStart="@dimen/status_bar_clock_starting_padding" android:paddingEnd="@dimen/status_bar_clock_end_padding" />
<TextClock android:textAppearance="@style/TextAppearance.StatusBar.Clock" android:textColor="#ffffffff" android:gravity="center" android:id="@id/clock" android:layout_width="fill_parent" android:layout_height="fill_parent" android:singleLine="true" android:shadowColor="#00000000" android:shadowDx="1.0" android:shadowDy="1.0" android:shadowRadius="1.0" android:color="#ffffffff" android:format12Hour="h:mm" android:format24Hour="HH:mm" />
<ImageView android:id="@id/notification_lights_out" android:paddingBottom="2.0dip" android:visibility="gone" android:layout_width="@dimen/status_bar_icon_size" android:layout_height="fill_parent" android:src="@drawable/ic_sysbar_lights_out_dot_small" android:scaleType="center" android:paddingStart="6.0dip" />
<LinearLayout android:orientation="horizontal" android:id="@id/status_bar_contents" android:layout_width="fill_parent" android:layout_height="fill_parent" android:paddingStart="6.0dip" android:paddingEnd="8.0dip">
<com.android.systemui.statusbar.AlphaOptimizedFrameLayout android:orientation="horizontal" android:id="@id/notification_icon_area" android:layout_width="0.0dip" android:layout_height="fill_parent" android:layout_weight="1.0" />
<com.android.keyguard.AlphaOptimizedLinearLayout android:orientation="horizontal" android:id="@id/system_icon_area" android:layout_width="wrap_content" android:layout_height="fill_parent">
<include layout="@layout/system_icons" />
</com.android.keyguard.AlphaOptimizedLinearLayout>
</LinearLayout>
<ViewStub android:id="@id/emergency_cryptkeeper_text" android:layout="@layout/emergency_cryptkeeper_text" android:layout_width="wrap_content" android:layout_height="fill_parent" />
</com.android.systemui.statusbar.phone.PhoneStatusBarView>

customize this line as u like

<TextClock android:textAppearance="@style/TextAppearance.StatusBar.Clock" android:textColor="#ffffffff" android:gravity="center" android:id="@id/clock" android:layout_width="fill_parent" android:layout_height="fill_parent" android:singleLine="true" android:shadowColor="#00000000" android:shadowDx="1.0" android:shadowDy="1.0" android:shadowRadius="1.0" android:color="#ffffffff" android:format12Hour="h:mm" android:format24Hour="HH:mm" />

thx to AL_IRAQI