c# - File/folders ownership in windows

Question

Hi, 

Ive been googling for a while but i found nothing so heres my problem:
I have to access system (windows) files, files are currently controled by TrustedInstaller. I tried few things like running my app as administrator, FileSecurity, SetAccessControl and many more that i cant even remember now. I know it can be done i just need a hint how to do it.
And before You ask, I need to access these system files to replace them to allow me running custom windows themes.

Cheers.

I manage to use takeown /f to get ownership but now cacls fails to give me full control over the files. It works in command line so Im guessing that my application dont have enough privileges. Is there anything else i can do to make this thing work?