Chosen Solution

Are the exterior buttons (volume, mute switch and side button) from the iPhone 7 Plus the same size and shape as the iPhone 8 Plus? Thanks.

I see no problem except your device rejecting the foreign buttons. They are both the same size and seem to connect the same way. They are swappable, just watch out for your device trying to reject the new organs. Cheers (why does every answer end in this way), Ethan