No, that may introduce new risks of things breaking, because each OS will be configured for the hardware it is seeing during install. It may work going from one device to the other but not the other way around.
You can take your working card out and make an image of it and write that to another card, and then put that other card back in the original device and use that for testing. If it breaks and all goes bad, you can simply swap back to the original card like nothing happened.
Maybe you could test a fresh install on the Pi 3 and get Pi-hole and your other apps up and running from scratch on that? It's a higher spec and sounds like it might be better suited since you're running various other software. If you do test on that, your existing install on the Pi 2 isn't being touched, giving extra peace of mind.
Same here, you can always manually override the DNS on key devices (eg a laptop, phone, etc) and simply stop using Pi-hole temporarily while you reinstall and test, if needed. For example, manually set them to use your router or an external service like 1.1.1.1. Then revert to how it was before to resume using Pi-hole once it's back up and ready.
No probs, the nice thing about the Pi is the ability to swap out the cards, so you never need to put a working installation at risk and can plan things a little more carefully. Good luck and feel free to post an update if you find anything interesting along the way.