Re-classing to 42a and moving to an instructor unit. Is this a good move?

If you're interested in AGR why not go onto active duty? On active duty, 42A warrants are always way under strength and they're always taking applicants.

Always remember to consider your quality of life. If the warrant officer area is what you want to do, I would suggest that you get your ducks in line (i.e. get the education and schooling required, if you have not already) and make yourself the "go-to" person in your unit.

What is your end state? Do you plan to stay in the military for any length of time? If I were you, I'd put together a 420 warrant packet and an AGR packet and develop both. Going warrant as a 42a is only difficult if you do nothing. Otherwise I'd go for it. I was a 42a at the Airborne School at Ft Benning (Regular Army) and at the Special Forces school at Ft Bragg (AGR). Both were awesome assignments. I enjoyed helping people so it just might be a good fit for you. As you put together both packets (420a and AGR) you'll probably have better insight on what you want to do. I hope this helps.