State allows our kids to do both.
I am learning to share better (I admittedly haven't always been good with it) but my biggest request is that you be honest and communicate with me EARLY what your schedule is like.
If you tell me beforehand (as in, the beginning of the season) that (example) you will be at US Finals on this day and need to miss this basketball game, I have no problem excusing it.
Don't tell me "Well, we do all stars but I won't EVER need to miss a game, so don't worry!" in April, then wait until basketball season to say "Oh hey I need to miss like 4 games because of Friday practices for Cheersport, sorry!" That's not fair to me because you most likely KNEW your gym was doing Cheersport in June.
My biggest rule is that all stars can't interfere with our comps or camp. You need to be able to be present for those if you want to try out.
I have good relationships with gyms around us, so HS practice is such that it starts and ends before the gyms start practice so I fully expect my girls to be at practice (we rarely go past 4:30/5 and all star practices near us start anywhere from 6 to 7:30.) If you need to miss or be late, use your demerits. If there is a repeated issue or some extenuating circumstance, it's okay to talk to me about it (ex: If you're snowed in at an out-of-state comp, there is nothing I can do about it. Just make sure you call or something so I know what's going on.)
I also have a rule re: missing games. This is school cheer. If you tell me you can NEVER cheer a game because of all stars, you're not really doing school cheer. You're doing all stars with some pep rallies and comps in it. All star kids are permitted to miss 2 games per season (2 basketball and 2 football.) Any additional games missed will earn demerits, unless you talked to me earlier in the season about games you needed to miss beyond that. (Our sports teams are not such that they make playoffs, so we do not have a ton of games.)
My biggest rule is that whether you're present or not, you're responsible for knowing the material. Ex: Even if you missed 3 summer practices, you still need to know the material to be ready for the game.
So in summary, advance notice and communication = EVERYTHING.