How to delete some folders from a BackInTime backup profile?

Basically I've added to exceptions a few folders that I didn't need a backup, that take several GB. Now, it's no longer updated, but the old snapshots still have it.
How can I remove it from old snapshots? A recursive rm for that folder name? I'm a bit confused because BIT uses file links to create the differential and don't want to mess it up.
As a bonus question, how do you backup the BIT folder structure? When I try getting it's size, it counts each file once per each snapshot it's in.
Thanks!