Will installing any of the ROMs mess my phone up if I already have things installed?

[TheLovatScout]

Hey, I've been wanting to change so much stuff with my HTC Touch Pro, but it seems a lot of the cool stuff lies within making ROMs.

I downloaded Total Command (all i did was switch my tab names) and advanced config (hoping to get rid of certain tabs and witch them around...couldnt do it)

Anyways, I was wondering if downloading certain ROMs like Mighty, KK, or any other one would really mess my phone up. I have the transparent flip clock installed, fonts, different keyboards and dialer skins. I'm afraid if I do instal these ROMs, it'll overwrite (or worse, try to and not succed, and mess my phone up) and I'll have to restore back to factory and lose all my numbers and such.

Any help?