For a LOT of imperfections you probably need to simply just recoat. But before you do do that perhaps you should consider if the the flaws are truly dust , ... or dirt particles from a dirty brush ... or simply old varnish
that is full of ''gel'' particles.
If you have a lot of surface AND your brush is the "dirt culprit" consider to use a super-high quality foam roller and then ''tip'' with a brand new badger brush.
As regards rotten stone changing the finish.... yes, anything you do may change the finish as blending in repairs
will always be somewhat noticeable, unless you uniformly and carefully rub the entire surface. I start with plain rotten stone and if then if a more coarse finish is needed, then switch to progresively ever coarser grades of pumice.
For a final satin finish final coat, for myself, I''d wet-sand the imperfect previous coats with 320, use a tack rag to very carefully & scrupulously clean the surface, and attempt a fresh coat with brand new, never opened varnish
. I personally never like the ''out of the can'' satin finishes and always hand rub .... starting with rotten stone, then pumice, then very fine bronze/steel wool, etc. .... and stopping with the coarseness that gives the best satin satisfaction (judgement call at the time).
Hope this helps.