No, no problem at all. The only time I've ever used separate tanks has been with 4x5 and my 1/2 gallon deep tanks and hangers (which work fine for Diafine.) For 35mm and 120 I always use one tank and just pour the A back in the bottle and pour in the B. Carryover of A into B hurts nothing (within reason of course.) It's getting any amount of B into A that you have to be careful not to have happen, and it won't in normal use.

It WILL reduce the amount of A solution. The instructions say to add equal amounts of A and B, discarding a little B, to bring up the total. So mix your gallon and divide each solution into two half gallon jugs. As the A solution carries over top it off, then add the same amount of fresh B, discarding a small amount of the used B. Say you need to add 2 ounces of A solution, but your B bottle is still full. Add two ounces of the unused A to top off the working bottle of A, and discard two ounces of the used B and top off with two ounces of fresh.

I haven't been bothering with this, just using it all from a big jug and that works fine too, but that may be why I do eventually have it "wear out" at somewhere between 50 and 70 rolls per quart. Next batch I mix I'm going to do what the instructions say. (In my defense I was introduced to it by a friend in the early 80s and he just re-used it like that, and getting more than 50 rolls through a quart seemed like a bargain. I didn't see much point in the replenishment scheme, and I was using quarts at the time, which were also pretty cheap, about $4 or $5 if I recall correctly.)