A change of reel sets would be a new version of the game, hence testing etc needed again. Despite popular beliefs no operator or provider possess the magical *Bloatgoat won't win today* button
A version of a game comes with pre defined set of reels, and those will be used for that game.
Games like jammin jars who runs on scenarios are of course different, but they still can't add, change or remove them as they feel fit.
A lower volatility version of a game for example will run a different reel set but legally speaking no operator can just switch these around constantly.
As for advantage play, no slot functioning as intended would offer such a thing. For example the oh so popular theory from a few weeks back of buying a certain feature a certain amount of times, will never guarantee a big win.
I don't mind people questioning the functionality of games. But I'm fairly certain most people agree that the thought of a industry wide conspiracy on all levels to gain an identical "advantage" to what's allready there makes absolutely no sense.
Furthermore if that had been the case, some whistleblowers would have emerged by now.
That said anyone who decides to gamble on unlicensed sites with pirated software have themselves to blame. And those sites do not reflect the standard and morale of the industry as a whole.