I would hesitate to do this. My thinking is this:

a) Even if some of your catalyst is coated/non-functioning, a reasonable percentage of it should be working. Thus, destroying a good percentage of the catalyst honeycomb is going to result in even less efficiency and more problems. I’ve done this on several motorcycles and never not had to go back and alter the fuel system, and I would worry the. ECU won’t have the programmed range to adapt.

b) the change will alter the back pressure as you well know, and I don’t know how the ECU is going to adapt to that, either.

So unless you actually have a physically clogged cat that is restricting flow, glowing hot, etc., I’d think it would not help and could make things worse.

Do you have the tall non-foulers installed, or the short ones? I have read that stacking two short ones or getting a long one (Dorman makes them in both sizes as I recall) is sometimes necessary. If none of that works, I understand your suspicion on non OE. I have never had satisfactory results from Walker or Bosal. I have heard that Eastern Catalytic is OK and you could check them out. Not a great answer overall, but maybe it helps refine your thinking.