[Ifti]

Could you not have kept the subscription from your Hero 9 and let it renew, and then got the reduced price on the Hero 10 for being a subscriber anyways?
Personally, I cancel my automatic renewal a month or so after purchasing the camera, just in case I forget later. It's something I never use anyways. I then purchase a new camera only after the subscription has fully expired on the previous year just to make sure it's expired properly.

GoPro support are rubbish - you won't really get very far with them unless you are persistent and keep contacting them! Their customer support do seem very lacking with what they can, or will, do!

So what is your current position?
You have the Hero 10 - did you get it at the reduced price, because you still had the subscription from the Hero 9 active?? It's just the subscription you're missing?

 

[Ifti]

I doubt the outside wrapper will stop the return

Some companies can be quite fussy and say the item has to be in resalable condition - ie, with the box etc.
That and the fact we all know what GoPro can be like! lol

I would still give it a try though!

 

[Ifti]

because the actual serial is on there and that will be the issue at hand.

Yes but the OP is not returning the GoPro because it is faulty - it will be classed as a 'change of mind return', in which case companies usually request it is in the same resalable condition.
Either way, can only try your luck. Hopefully OP will come back and report what happens