Blind Signal separation vs .... what?
The opposite of blind-signal separation is not "non-blind signal separation". The thing is, depending on what you know on the signals you will use different algorithms.

For example, if you know that there is a low frequency signal mixed with a higher frequency one, you can use low/high-pass filtering to get the two signals.

There's no real name for what you're looking for because every case is different. The generic way is more or less filtering the signals with the information you know. But the filtering is always different.