Studio 2014 - How to change segmentation rules (no break after colon)

(This is a cross-posting from Proz.com, but I received no answer there.)

I am trying to import a .TMX file from another CAT system, and Studio is breaking after the colon, which my .TMX does not, so I am not getting good matches. I do not want a line break after the colon. I have tried to change the segmentation rule, but it's not working. Studio seems to allow you to add a new exception rule to break after a certain character, but not to remove one that is in the default. Any suggestions? (I don't know anything about regex.)

Thanks