Have you ever reversed your opinion on a piece of gear?

Yeah. My Decca (London) Super Gold cartridge. I was actually going to throw it away after mothballing it in 2000. It never worked well on my LP12. Ten years later, I refurbished it and put it on a 401 and love it and would never part with it.

Interesting question.   I think I'd have to answer:  No.

My general assessment of a piece of gear has always remained fairly constant.   Even when it comes to speakers,  if a speaker doesn't have an "it" factor for me very quickly, I never really find it no matter what other set ups or conditions I hear that speaker in.  

Who hasn't,?

Technics EPC-207C cartridge. Came back to it over twenty years later and realized it was way better than what I had replaced it with because I thought it was crappy the first time around.

Very probable if your have two different listening environs.