Windows Vista Patching Theme Files

Does patching the shvcs.dll ,themeui.dll and uxtheme.dll (I think theses are their names,I'm going on memory ) cause any problems in Vista Home Premium SP1?I like to be able to change the look of windows now and then.

 

I know I've done it properly.

The first time I put Vista on and installed SP1,I also patched these files,every couple of days I was getting a blue screen of death,the PC rebooted and told me it had recovered from a fatal error.
I hadn't had any blue screens before SP1 was installed.That time it was a standalone version of SP1 I installed,this time SP1 was offered in windows update,I know it's probably just the same but I was hoping that because update offered SP1 that it might be more stable.

Anyway,the only thing I had modified before were those theme files,I can't think of a reason that these files would cause a blue screen but I'm no expert.
If I remember the report after each crash said something about a couple of files in User/Appdata/temp and something in windows minidump had been responsible for the crash.

I have had SP1 on for one day now without any crash so far.It had happened by now the last time I put SP1 on.