In current, classic approach to move teaching system, it is quite annoying to make changes to pokemon moveset, which discourages players to experiment with various moves in PVP.

For example : If I want to swap Flamethrower with Trick to Togekiss I have to travel to tutor in Johto. To revert that change I have to go get and buy flamethrower TM again. 

 

Suggested sollution :

Metadata of already taught moves stored for every pokemon. NPC that allows to access this metadata and relearn stored moves freely, or for symbolic price. 

This will also add another quality to pokemon economy - amount of moves stored in its memory.

I would also like to suggest analogic sollution for already trained EVs

Mmm, my thoughts on this:
 

The suggestion regarding moves is understandable and somewhat acceptable. If a Pokémon once knew a move, wanting it to remember that move again is logically reasonable. It would also make team building and experimenting with sets much easier and more convenient.
 

However, for EVs, I don’t agree. It doesn’t really make sense. EVs represent the result of training effort invested into specific stats, so they shouldn’t be something a Pokémon can simply switch around freely. That would not be logically consistent with how EVs work.

For Legendaries, where options can be more limited, allowing some flexibility may be reasonable. But for regular Pokémon, I don’t think it should apply.