I have just purchased some proper Resin for my D7 DUP printer which is a rapid cure resin especially for these printers. I have been using it as a glue to assemble some of my models, but also I have been mixing it with baby powder to make a filling paste. the amount of powder depends on how stiff a a filler I need. You can use it on those prints that have bits missing. or building up areas that you wish to change. I have a 3w UV led mounted on a large bodied pen that I use to cure the filler. Standard resins should work the same just take a bit longer to cure.
It is also best to use a clear resin for this as the UV will penetrate a lot further so you cane build up with thicker layers.