Until they change their minds again, the Mets have made a decision – hopefully definitive for at least the remainder of the season – on Jenrry Mejia.

The prospect with the million-dollar arm will remain in the bullpen.

Manager Jerry Manuel confirmed last night what many surmised after Manny Acosta was optioned to Triple-A Buffalo instead of Mejia to make room for Ryota Igarashi’s return from the disabled list.

“You have a young man who has a tremendous arm, tremendous upside,’’ Manuel said. “If you take what he gives you in small bits, it’s very serviceable, even at the big league level.’’

Several things went into the decision, notably when Mejia started altering his delivery Thursday in Washington. Altered deliveries lead to arm problems and the Mets want to nip possibility early.

During the series with the Nationals, Manuel had suggested Mejia was likely to be the one to go to the minor leagues to make room for Igarashi.

Starting might still be in Mejia’s future, but not for now, and you would be correct if you thought this move had something to do with Manuel’s immediate job future.

“If we wanted to have him start, he could start in the winter somewhere,’’ Manuel said. “But here, if he’s serviceable and if he’s usable, then I’d like to have him. It’s probably selfish on my part, but that’s how I feel.’’

With Igarashi back, the plan is for him and Feliciano to work the eighth and Mejia to work the seventh. Watching Mejia blow away Mark Teixeira Saturday night convinced Manuel.

“Basically, that was the plan all along,’’ Manuel said. “We felt that Igarashi could handle the eighth, and we needed someone to handle the seventh. I wanted to see Mejia pitch in this environment and see how he responded to it, and he did real well.’’

I only hope the Mets stick with this decision and not waver. To bounce him from role to role at 20 could be harmful to his development.