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

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.  

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.

As a former dealer, I have reversed my feelings on a piece of gear many times for different reasons.  For example, as I have posted here before, EVERY piece of Nakamichi I sold broke within 2 weeks and had to be sent back for service.  They came back fine, but as a dealer, I had a TON of very unhappy customers, some of whom paid big bucks in the mid-1970's for this gear, and were NOT HAPPY.  That made me NOT HAPPY, so even though the only difference we could hear on an A-B with a direct-to-disc Mayorga record and the NAK 1000 was a slight "hollow" characteristic to the music, I changed my mind about Nakamichi's product quality control, thus the brand.

Other items--someone brought in the Marantz (RIP, Sol) early stuff--7's and 8's and so forth--and it sounded pretty bad compared to the Audio Research stuff of the day.  Doesn't mean I did not like Marantz--I sold a ton of it and it did NOT break--but I was let down by the earlier technology on speakers (Maggies/Fulton 100's) of those days.

As far as having something change as you listened to it over time in the store--weeks or months in some cases--sure, some characteristics and idiosyncrasies reared up in pretty much every component.  We had to decide if they were positive or negative and make decisions on the future from those impressions.  For example, BOth Crown (400) and Phase Linear (400 and 700) amps were very sensitive to load, sounded very "trebbely" and strident on some music, but were very powerful amps in those days.)  Sherwood used to make very nice tuners and receivers that never broke, Mc stuff was not very good regarding sound or dependability compared to some other high-end brands--Audio Research, Bryston, etc.

When a manufacturer was hard to deal with and gave me hard time, I would drop them, so I may have made a product decision based on BUSINESS rather than sound, and deleted these brands from my inventory. When you came to shop, you might ask where that brand's stuff was, and I would tell you.

It is a tough business, and even more so today when no one wants a good sound system any more.  My 23-year-old daughter will not even let me set up something in her apartment; they are fine with whatever they hear on whatever devices they use today.  Glad I am not doing that for a living any more!