Jo , i have not a problem with this and i change those settings without a problem while rendering.
I always thought about things like you said above
and make these changes in a cautious kinda way.
But just for your knowledge; the real reason i change those settings is that TG2 uses the cores
very aggressively unlike lightwave for example.
I can leave the 8 core settings intact in Lightwave and surf and use the other small programs without much problems.
But TG2 makes such an impact that i always leave 1-2 cores for other things .
This was the same on Vista (64 bit) and now on Windows 7 (64 bit), before i had only 4 GB ram and now with 32 GB ram.
I do not know why this happens and this is not something i think very much about , but i just wanted you to know