If you mean for trade-in for Dil, you've to have levelled that Rep to T5 IIRC.
"You don't want to patrol!? You don't want to escort!? You don't want to defend the Federation's Starbases!? Then why are you flying my Starships!? If you were a Klingon you'd be killed on the spot, but lucky for you.....you WERE in Starfleet. Let's see how New Zealand Penal Colony suits you." Adm A. Necheyev.
I usually try to keep some of the elite currency on hand with the reputations that use them because it is used as part of the price for the reputation sets and whatnot and you never know when something like that can come in handy in a pinch. I have quick-bought things for doing endeavors and picked up Burham's vac suit when I was short one for a mission for instance.
Comments
Looks like the OP is talking about exchanging elite marks of one reputation for the elite marks of another reputation.
Currently, there is no such system in the game.