We're currently using MT3.x, but upgrading to MT4.x. I have successfully performed the upgrade in our test environment, and upgrade went very smoothly.

I noticed, however, that static archive URLs have changed from a using underscores_as_separators to using hyphens-as-separators. Is there a way to manually change this back? We have a lot of direct links to our blog entries indexed by search engines, and I'd hate to break all of their links.

After a bit of googling, I saw that someone successfully did this in 3.x (I believe the file was in Util/), but didn't reference exactly where the change would be made.

Does anyone know where the word seperator for archive URLs is defined? Thanks.

Archive Mapping, under Template Options for each of your archive templates. I'm not aware of a way to change them en masse.