I don't think there is any set in concrete rules as every barrel is different. My TX200 .177 doesn't show any problem with changing brands apart from the P.O.A. in most cases. A Pro Sport I once owned took at least a dozen shots to settle down after a pellet change. I've owned FWB .22LR match rifles that were similar.

The other day I changed from Accupell to JSB Express, no change apart from the P.O.A. The Express grouped as well as ever from the first shot. Same in reverse and same with AA Fields and Edgun 8.4gr. After cleaning the barrel, the rifle groups straight away. Mind you, it's a particularly accurate TX200, although that may have nothing to do with it.