how to undo a rom modification

[AStrayDog]

first of all i'm sorry for this question :wink:
I'm really a beginner in modifying my extended-rom. I want to change my mda to a "xda". i've got the latest updates and some of the software discussed on this site but there is one question left:
Just in case i make a mistake while modifying my (extended)-rom: can i repair everything by simply installing the original update provided by t-mobile??
Thanks for any answers, help, suggestions,...

Andi

[edsub]

Simple answer: YES.
Before you start 'modifying the rom' or 'upgrade' you should make sure you have an upgrade package from the original operator for the rare ocasion you need to go back (then you can upgrade it back to something they will recognize. Imagine how T-Mobile personell will look at an MDAII that has all the O2 stuff on it).
In your case: Make sure you have the T-Mobile 1.72.190 rom upgrade at hand while you upgrade to a O2 rom