It must been a work to fill 111lbs of
LR in 55G unless dense LR! Thats lots of LR for 55G. Any pic of tank/system?
You can have aggressive fish chill out in isoaltion quarter when new are introduced but question is, is it possible with all the rocks. If gonna go thru removing rocks to catch couple of damsel (nightmare,lol), would not bother.
On the other hand, you can
acclimate and put new fish in
DIY contraption (isolation container) to have new fish settle w/o any harrassment due to aggreassive future tankmates. It has to be big enough with holes, lots of holes for circulation, so fish can move somewhat. LMK if you need ideas.
When ready to release fish, do it at night when all the fish are chlling/sleeping in the rock thus new fish will have better chance to adjust so either can fight back or learn to utilize the rock to hide/run. Be gentle not to spook new fish.
Since reef, doubt you will get any large fish.
BTW, damsel sare
USUALLY aggressive towards each other unless love at first sight. LOL! So keeping few will keep themseves busy.