No problem moving those swim workouts to any day you want. Not just Saturday’s, but any given swim can be moved. Unlike the bike and run, swim workouts have very little impact on the rest of the day. Of course, it’s best if you don’t have your swims all occur 3 or 4 days in a row, if you can spread them out a bit your training will be more effective.
Had never considered rotating easy/hard but makes total sense.
Never go more than two days between swims. Once had a swim coach say that after two days you start losing fitness. Not sure if that’s true or not but I’ve always stuck with that. That was some 40 years ago.