Go ahead I guess? It's already a bit annoying having to completely overlook Pokemon because of how long it would take to train them, so I wouldn't really get in the way of a relatively minor cost reduction.
At most, someone would save what? 2 Pokecoins if they had three different Pokemon they wanted to try and train before the game ended that could all learn that one TM?
Edit: Yeah, they'd only save 2 poke coins then, since they still have to buy it the first time.