Hmmm... sounds like something was corrupted in the startpos. I would suggest first off you revert to the back-up copy you saved before making any start-unit changes (you did, didn't you? ) and try changing them one by one.

Also, what were the complete symptoms? Namely:

1) Did you check EVERY faction?
2) Did you try going beyond the faction selection page (ie hit "Start campaign")?
3) If 2 is a yes, then what happened next? CTD or successful start-up without any units?
4) Did you make any other changes - eg to unit names in the names.txt file, or to the unit_prod?

If you do get any crashes, make a note of the error message. Useful tip: if the error message is not visible (ie window at the back) and the game freezes, then alt-tab out of the game and back into it, this will bring the message window to the top.