Sure. "Over-regulated" means someone who has their emotions under too much control which causes a problem for them. For example, they may feel just "blah" or like they aren't really living, or their significant others may complain that they are cold or distant. In that case it may make sense for a T to really encourage them to feel more.

"Under-regulated" means someone's feelings are all over the place which is causing problems for them. For example they may be in crisis, crying a lot or acting out in anger. In that case it may make sense for a T to help the client distract herself sometimes or get some distance from her feelings. These are the kinds of people who DBT is designed to help for example.

Really it's not that simple since some people may have a combination of both, but it's just one way of looking at things.