Moving custom field data

I imported a bunch of entries from an old blog into a WordPress site I’m putting together. However, during the import, I routed a custom data field from Movable Type to the wrong field in WP.

I was wondering – can something like this be done? If so, how?

Look at the custom data field for the MLBURL custom data field, and if it starts with a number (any number, doesn’t matter), change the custom data field from MLBURL to UNIFORM? Can that be done all at once?

I have a few thousand entries that properly use the MLBURL custom field, so I can’t just brute force change ’em all (all the real ones start with the letter h (as part of http:). That’s why there has to be a conditional.