Unfortunately, this is not possible; so much about league settings that we import depends on team names. The only way we can guarantee these are accurate is to write them into our database every time your league is synced. We don't want to allow users to make any changes that are periodically overwritten by our servers, so for this reason team names are not editable.
If you wish, you may manually enter the league and its settings, outside the league sync system; when adding a new league, scroll past the list of fantasy football providers and enter the name for the new league in the textbox, then hit Add.