If it were a single strain of saccharomyces, sold by a lab, then it would change over time and "adapt" to a specific brewery environment. Well, all yeast will change and mutate over time. I'm a bit torn on what to believe yeast labs are telling us about how many times we can viably use yeast. They are in the business of selling yeast, so it makes sense that it would be suggested yeast be discarded after X generations and a new pitch be purchased. Please bear in mind that my opinions reflect our use of a multistrain culture. I realize that drift in yeast character is probably undesirable if you're brewing a Czech lager (which is what I like to drink as much as saison). Yvan from De La Senne mentioned to us recently that their strain of saccharomyces has been through 35+ generations with the only noticeable difference being a bit of cloudiness/flocculation.
With our house culture, consisting of many different yeasts and bacteria, there are different "tricks" we can do to keep bacteria from taking over the fermentation profile since bacteria tends to reproduce faster than yeast...if the yeast is sluggish. We pitch our yeast from cone to cone, batch to batch etc. If we don't have yeast available in the bottom of a tank, we will step up the culture from our yeast brink. Every so often, if we see the culture presenting more acidity than we want in a beer, we can cycle a pitch through a hoppy beer, like Wytchmaker, or El Cedro. Hoppier beers will inhibit lactobacillus growth. Also, I will save vials of yeast from fermentations that present really great/desirable character and re-introduce them to the yeast brink, and often to 3bbl and 6bbl starters that will be pitched into 30bbl or 60bbl batches.