First be polite and willing to work with the FAs and GAs because assuming they're on your side generally goes better than spoiling for a fight. And FAA rules are on their side for keeping it in-cabin if there is friction:

https://www.transportation.gov/brief...travel-musical

If it's possible to buy earlier boarding, whether standalone or in conjunction with C+, I'd go for that in the name of increasing the odds of finding space in 'space available'.