I'm not aware of any way to backup the current ROM in case of problems. I'm also not aware of a way to just upgrade the GPS but there may be one that I couldn't find. My head spun too but I walked through it and now have an awesome phone. Here's the things I went through:
http://www.ppchaven.com/viewtopic.php?f=19&t=4 - this thread gives excellent instructions for how to upgrade the radio on the Verizon XV6900
http://wiki.xda-developers.com/index...VerizonAGPSFix - then for quick GPS acquisition you need to do the stuff in this wiki, your GPS will ROCK!
using buildos from PPCKitchen.org you can put in the office applications, and everything else you want to have in there. It will probably take you a few tries to get everything in there that you want to have but IMO it's worth the effort. Otherwise you could just use someones prebuilt rom that has everything your looking for.
I'm currently running the 20273 kitchen, btw.