Can you return/exchange an item at any Walmart store when it was purchased at another Walmart?

I believe so

Yes. It doesn't matter which Walmart you purchased the item. You can return it anywhere. Even if you are in a different state. Take it back to any Walmart anywhere in the Continental U.S.

Yes as far as I know you can, however I recently returned an item from another store without a receipt, Walmart no longer gives "in store credit" for "no receipt" returns, they did allow me to exchange for another item(s)... (This was in a Eugene, OR store)

Yes

Most often times, stores will be accommodating with the tags still attached and a receipt. I've been able to do returns when I had items purchased in another state and no receipt. I received credit for the full amount on a card that had no expiration date attached. I used it in that store, so I am not certain if it could've been used in a different store.

As long as you have the receipt I believe you can except the one at gateway might not if it's not something they carry.

Yes, you just need the tags. If you dont have a receipt you need the card you purchased it on. If u paid cash they may have a limited policy like exchange or reduced store credit