Unless you are an experienced driver that goes up to very high speeds and utilize the brakes to their absolute maximum, changing pads on the same rotors should not be a problem.
I personally do not change them. I use Porterfield R4S pads that are street/auto-x compounds. However, i am certainly not a terribly fast driver and probably do not use the brakes as hard as some experienced drivers do. The R4S are handle my needs quite well.
About a week ago, however, at the track I used the stock pads to see how they would perform for my needs, and it was disappointing. They baked on to the rotors turning them blue. I have not changed to R4S on the STi yet, but I suspect, I will have to either resurface the rotors or get new ones. Porterfield might be comming up with slotted OEM replacement rotors for the STi soon, if they do, I'll be switching to them.
I ran my 1st event with OEM pads and got considerable fade so I switched to Carbotech Panther + for the next event. When I went back to my OEM pads I don't have very much stopping power like there's no friction.
I also have dark rings on my rotors where there's uneven material build up. I did try and bed them again but it was not use.
I'm not sure what to do next? I don't really want to turn the rotors or buy a dedicated track set.
I'm assuming that the Carbotech's are not compatable with the OEM material
You'll have to let me know how your next event goes.