question on customised techniques

[WhiteKnight01]

If I have a level 10 technique and I learn a customized technique does it overwrite it completely or does it just add the merits and demerits to that level 10?

also what can do I do with all the customized techniques discs that I wont use?

[Sandmind]

The merit and demerit get added to the tech, so you can sefely learn an higher level and keep the change. Cannot decompose those unused disc, so it's eitehir npc'ing or discarding.