So, you're going to split up the pairs, let a new pair form, and then split that up? Seems stressful at best for something that both may not work and may not be needed. Why not just... give them a BTA and see if they take it?
You're also likely to run into problems with the sexes, particularly if you keep the individuals separate for long enough. You'd have to be very sure not to have two females in the tank, or two males, because then one of your males would turn into a female.
To top it off, split-species pairs don't always work, and there's no guarantee they won't leave the anemone for something else.
By "they'll fight", I mean you can't keep two pairs of clownfish in the same tank unless the tank is massive. You'll wind up with one pair.
I would keep the two pairs separately. If you find that the Percula won't go into the BTA, then I would switch one of the pair. Once the switch is done, you will have a female Ocellaris that is hosted by the BTA and a male Percula that will learn. In the other tank you have a male Ocellaris that living in a BTA and a female Percula that does not, she will learn. Once all the pairs are into the anemones, you can do a switch back.
BTW, changing pairs like that is no problem. I did this all the time. I used to breed clowns. They won't miss a beat.