I would say the sweet spot for defining your users rights is right after you gain some major traction and before any kind of exit is even on the horizon. And definitely before other companies start to rely on you, and/or network effects have put you in a position where you can afford to screw people over.

Probably it would be a good idea to have your business model figured out as well.

A side effect of this is that it may force you to think a bit harder over whether you want to support this creation for an extended period, and that alone might be enlightening.

So, pivot to your hearts content, but when you feel you have a 'live one' define your users rights and stick to it.