Add/remove theme support to/from programs that have not it. For example, if you add theme support to "...\System32\mmc.exe" and then you open your "Computer Management" console, it will look full-skinned. Note that some old programs may fail to start or display graphical errors when skinned; if this occurs you can remove theme support.
Set the desired priority to all running processes (also system ones). For example, you can run "Windows Media Player" at high priority without having to change it manually from "Task Manager" every time "Windows Media Player" starts. Note that setting to realtime the priority of an heavy process may cause system to hang-up.
Replace in-use or system files. For example, you can replace "notepad.exe" with the executable of another editor. Please note that replace system files is dangerous. Do it at your own risk.