I have a Kolsch, Saison, Scotch and Wheat that are repeats, I love them as I have them. For the Wheat and Kolsch I think they are less fun to experiment with since they are pretty straight forward and I know how I like those styles. I keep the Scotch recipe the same because it takes me a year to burn through a keg of it. I know I like this recipe, why risk changing it up? Saisons are a little different, again I love my saison recipe and brew it regularly but that's a fun style to play with since you can do so much with it so I have my goto then also change things. Hoppy beers are always different, they are my favorite style and the one I brew the most often and I'm always playing with something new. I'm currently running through all of the Cryo hops with the same grain bill and bittering charge, just changing out the flavor and aroma hops. I also have a Rye IPA recipe that I love but am always tweaking something each time I brew it.
I guess you could say I am always changing something with each iteration of every beer, as I learn new things I implement them hopefully making each brew better then the last. A pretty normal progression for most brewers I think is using tap water, using tap water with minerals and finally building water from distilled/RO, improving temp control from a steady closet, to a swamp cooler to ferm chamber, going from pitching a yeast pack to pitching a starter, finding ways to minimize O2 exposure, etc. The recipe may remain the same but I'm far from being at the point that the entire process is under lock down. I never have two kegs of the same beer on tap so consistency is difficult to evaluate, and frankly I don't care because I don't have customers who have come to expect a certain product. I get to decide if "improvements" actually make a better beer.