[LG Optimus Black] gabwerkz:
Anyway, I started the project for a theme in CM7. It's a WIP. :)

A Theme for CM7 will only modify/add what you modified/added. Leaving everything you didn't touched intact. All drawables (images, animation etc) will be redirected only to specified system apk and replace that specific file. Unlike SystemUI and framework-res modification, it will overwrite/replace the whole apk.

Example:

<?xml version="1.0" encoding="utf-8"?>
<resource-redirections>
<item name="drawable/battery_low_battery">@drawable/com_android_systemui_battery_low_battery</item>
<item name="drawable/stat_sys_wifi_signal_4_fully">@drawable/com_android_systemui_stat_sys_wifi_signal_4_fully</item>
<item name="drawable/stat_sys_wifi_signal_3_fully">@drawable/com_android_systemui_stat_sys_wifi_signal_3_fully</item>
<item name="drawable/stat_sys_wifi_signal_2_fully">@drawable/com_android_systemui_stat_sys_wifi_signal_2_fully</item>
<item name="drawable/stat_sys_wifi_signal_1_fully">@drawable/com_android_systemui_stat_sys_wifi_signal_1_fully</item>
<item name="drawable/stat_sys_signal_4_fully">@drawable/com_android_systemui_stat_sys_signal_4_fully</item>
<item name="drawable/stat_sys_signal_3_fully">@drawable/com_android_systemui_stat_sys_signal_3_fully</item>
<item name="drawable/stat_sys_signal_2_fully">@drawable/com_android_systemui_stat_sys_signal_2_fully</item>
<item name="drawable/stat_sys_signal_1_fully">@drawable/com_android_systemui_stat_sys_signal_1_fully</item>
<item name="drawable/stat_sys_r_signal_4_fully">@drawable/com_android_systemui_stat_sys_r_signal_4_fully</item>
<item name="drawable/stat_sys_r_signal_3_fully">@drawable/com_android_systemui_stat_sys_r_signal_3_fully</item>
<item name="drawable/stat_sys_r_signal_2_fully">@drawable/com_android_systemui_stat_sys_r_signal_2_fully</item>
<item name="drawable/stat_sys_r_signal_1_fully">@drawable/com_android_systemui_stat_sys_r_signal_1_fully</item>
<item name="drawable/stat_sys_data_fully_out_h">@drawable/com_android_systemui_stat_sys_data_fully_out_h</item>
<item name="drawable/stat_sys_data_fully_out_g">@drawable/com_android_systemui_stat_sys_data_fully_out_g</item>
<item name="drawable/stat_sys_data_fully_out_e">@drawable/com_android_systemui_stat_sys_data_fully_out_e</item>
<item name="drawable/stat_sys_data_fully_out_3g">@drawable/com_android_systemui_stat_sys_data_fully_out_3g</item>
<item name="drawable/stat_sys_data_fully_out_4g">@drawable/com_android_systemui_stat_sys_data_fully_out_4g</item>
<item name="drawable/stat_sys_data_fully_out_1x">@drawable/com_android_systemui_stat_sys_data_fully_out_1x</item>
<item name="drawable/stat_sys_data_fully_inandout_h">@drawable/com_android_systemui_stat_sys_data_fully_inandout_h</item>
<item name="drawable/stat_sys_data_fully_inandout_g">@drawable/com_android_systemui_stat_sys_data_fully_inandout_g</item>
<item name="drawable/stat_sys_data_fully_inandout_e">@drawable/com_android_systemui_stat_sys_data_fully_inandout_e</item>
<item name="drawable/stat_sys_data_fully_inandout_3g">@drawable/com_android_systemui_stat_sys_data_fully_inandout_3g</item>
<item name="drawable/stat_sys_data_fully_inandout_4g">@drawable/com_android_systemui_stat_sys_data_fully_inandout_4g</item>
<item name="drawable/stat_sys_data_fully_inandout_1x">@drawable/com_android_systemui_stat_sys_data_fully_inandout_1x</item>