Easy. In Chess, where the Elo system originated, there are lots of different Ks. No problem whatsoever, if you want this. OP obviously doesn't.
Thanks, the issue is that should recalculate everything, but would be cool, there are limits to the value of K?
Of course that it is possible, but why, what's the point doing that in Elo system?!
Official ranking system already does that, and this is the other way to measure performance.
And as amirbachar pointed out, this system gives better predictability of head-to-head accounts.
Easy, I don´t know much about chees, but tennis not is like other sport like boxing for example, because many times, the top players use some tournamentes as preparation for Grand Slam on M1000, and many times they lose matchs that they would not lose in other tournaments..