I agree with PP, if you can adjust your ADR's then do it, but if nothing is available, keep what you had before.
when the no show fee was first added, we were told even one person not showing would = a fee, but I think WDW has adjusted their policy. Personally, we mostly stopped making ADR's.
I've not used the military discount, but one thing you can't do is change the LEAD person on the room reservation. I'm also 100% sure, If you have a military discount, the person w/military ID has to show their ID. If not ,your room will revert to rack rates.
Otherwise, you can probably drop anyone else with no problem. As someone else said, if you have a suite, then I don't think there is an extra adult fee. If you have a Mermaid room, then WDW charges a small fee for the extra adult. ( I think it is $10 a day at the values)
But if you don't have any tickets or dining, then you may not see any difference either way. The only thing different is that you would get a magicband for that person.
If the no show guests has tickets or dining , then dropping them would = a reduction of their ticket and dining plan costs.
Talk to Disney!