Actually, the ODB file you mentioned only affects changes to the RSS, and nothing special is done to the radio's codeplug (as far as I know). Thus, a codeplug from an MTX9000 already on the ham bands isn't going to do you any good, because the software will still gripe when you try to put in your own frequencies as long as the ODB file hasn't been modified.
If you're not certain about your hex editing skills, just copy the whole RSS directory to a new location, so that you have two identical copies of the RSS. Then, you can hack on the ODB file all you want, and if you screw it up you can just re-copy the good ODB file from the original directory. Also, you don't have to worry about screwing the radio up for the reasons mentioned in the first paragraph--the ODB file doesn't affect the radio.
Unfortunately, I think it was decided that the sharing of such "pieces of RSS" as ODB files is not kosher according to the big /\/\, so you're going to have to edit the file yourself. But, it's not that hard...
http://www.batlabs.com/mtsx.html
Good luck and have fun with those radios--I own one and have worked with several, and they tend to make pretty nice 900MHz ham radios. Sounds like the price was good, too