Replacing soldiers with unique skills

My Support Unit's staff can be divided into two categories: ultra-competent endgame soldiers of rank A++ and up, and a handful of early-game interpreters with ranks as low as C. Those interpreters are dragging down my Support Unit's level, but aside from the Afrikaans guy, I've never been offered an opportunity to replace them.
What options do I have to get better interpreters? If I fire them (can I fire them?), will the "Extract Interpreter" side ops come back? Is there any way to get replacements without losing my existing interpreters, so if the new ones suck worse than the originals, I can keep the originals? I'd imagine that FOB invasions might also be an option, but everyone else's interpreters probably suck too.
(This also applies to the Legendary Gunsmith and anyone else with an important skill you only get one of that I might be forgetting, but my Legendary Gunsmith is A+ rank, so he's not dragging down the R&D Unit as hard.)
Best Answer
For every "_ Specialist" or Interpreter you get in Main Ops, you can redo the main ops and re extract them, they usually have better skills than the first time you did the mission.
For the Legendary Gunsmith, I don t know how you can redo his side ops.
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Answer 2
You can assign them to a different team or the "waiting room".
While you can replay main missions, I do not think you can replay side-ops in general. However, if your Legendary Gunsmith were to be either killed or extracted then you might be allowed to re-do that mission.
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