Older GFWL titles activation limits?

I’ve been picking up a few PC games lately that are Games For Windows Live cause the achievements stack with the Xbox ones for the same title, and I enjoyed the games enough to play twice (if the price is right). Thing is, I have some older titles too, like Halo 2 and GTA4 which I’ve heard have an activation limit, whereas newer ones don’t. What I’m wondering is if there’s a way to get around the limit itself by patching the game so long as you use your same valid key to sign into GFWL when you actually play. I got the impression that the MF.dll for Halo 2 being replaced allowed the game to run and still sign into GFWL. I’m wondering if anyone else knows anything about this. I had my GTA4 installed once, but I chose to patch it rather than activate anyway, just on principle. I got tired of activation limits back when I had Office 2000. The modding community for the trilogy was great, but GTA4 was lacking so I decided to play the 360 version instead. I’d like to know what I’m dealing with since I’m thinking of ordering some other GFWL titles. If I’m going to have issues with older ones cause I reformat my machine, upgrade, etc every so often, I’ll avoid them.