[KilgoreBA]

HD Tweak will function but I would be careful as to what you use it for. Anything that messes with your actual phone/data/GPS settings could cause you to have to Hard Reset your phone.

As for some of the other features of HD Tweak such as Bluetooth, Security, Volume Control, Lock, Title Bar, Camera, Startup, Internet Explorer, HTC Applications, Diary, and GSensor- these will work fine. Just be careful what you tweak. As you said, GSM and CDMA are quite different.

Pretty much any software made for the HD will work, as long as it doesn't mess with your actual phone/data/GPS Settings. Also, most software that is made for WVGA screens works really well. Hopefully I answered your questions.