I think you should be able to reborn into another KG and it'll erase the current one if they are the same type of KG.
For example, Master (3 reborn) Hyuuga wanted to switch to Uchiha.
Reach 80 DKs and select Uchiha as reborn and it'll erase ALL Hyuuga reborns because both are Doujutsu.
I don't think it should cost anything else (No not even DP) because you're already at a setback by trashing gained reborns.
Honestly, I wouldn't care about swapping reborns if there weren't certain techniques only available to certain KG combos.
<.<
Considering how many KGs are now available, I don't know how many secret combo techniques there could be and how useful or powerful they are in the forest.
Well, I would like an option to swap KGs because they are, for the most part, unknown unless you actually have a char with it or know someone willing to spill the beans, so people choose blindly.
I'd like to try a KG out and if I don't like it, I would like to trade it instead of having to give up on my character.
Even then, the power of the KG varies with the number of reborns, so giving up on a KG early can be detrimental.
Oh, I am also for just purely erasing KGs because not being able to control the Attack on your Weapon can be annoying.
If we take this route, then it can be DP cost related.
P.S.
IMO, the two best KGs are the Doujutsu by far as I can tell at the moment (Rinnegan and Sage Mode could be better). Even then, Uchiha is way Over-Powered compared to Hyuuga. Not that I want Sharingan, but rather peeved at the imbalance. >.>
Sharingan needs a nerf. =P
Or Byakugan needs a buff.
The rest of the KGs seem to act like filler, just saying.