i bet there is some rule that you have to non-tender (e.g. make them available to every team) players that are on the 40 for the rule 5 draft. you can't just take them off after the draft and send them to the minors while retaining control. that'd make sense.
so assuming that the royals know they'll be signing at least 2 players that will need to go on the 40, they'd either have to expose calixte now or at the time they sign the second free agent. now might be preferable since there are lots of other players being exposed at the same time. maybe.