Can i stack gifted gamepass codes?

Yes, if you add a pre-paid subscription to existing subscription, it will extend that time out to encompass the full time.

If you are on a TRIAL of Game Pass, and you add a pre-paid subscription, it does end the trial and start the subscription, but you shouldn't have any issue stacking pre-paid subs onto your account. Just make sure you're signed in to the right Microsoft
Account when you're redeeming the codes so as not to put them on the wrong account.

They should stack. I usually do this for Game Pass and Xbox Live Gold, whenever there's a cheap offer somewhere, I tend to load up on codes so I'm set for at least the next year.

Yes you can stack prepaid codes. My live and gold are good until 2021

Absolutely you can stack them and use them as needed.

I just wanna know how to make posts, I want to ask if there's a way to get these reward points faster like a family or whatever so I can get gift cards