Epoxy Barrier coat
Putting an epoxy barrier coat over a properly applied epoxy laminate is like wrapping a plastic bag in a waxed paper bag. Depending on whose products were used and how they were applied, there are few plastic materials that are more water impermeable than epoxy resin. Un-thickened epoxies (like WEST System, MAS and System 3) work best with final overcoats of their own epoxy resin.
Putting another product over this layer is un-necessary and frankly potentially less successful.
In my opinion the only reason that the epoxy paint (which has pigments and solvents and therefore is more permeable than the resin) is added is to provide a "marker" coat so you don''t actually sand down into the epoxy resin coats. Also, Epoxy does not stand up to UV very well and so the epoxy paint coat acts as a sunshield to protect the epoxy resin should there be a time when the boat is out of the water and the raw resin is exposed.
I do question the replacement of only the gelcoat as a proper repair method. Rarely is the problem only in the gelcoat. Usually the problem is actually in the laminate below the Gelcoat. Merely replacing the gelcoat with a an unreinforced resin (or barrier coat) layer rarely solves the problem. Most qualified repair people that I have talked to seem to suggest at least a single layer of epoxy reinforced with glass cloth as a proper cure. The gelcoat layer is too thin to provide a thick enough and strong enough repair to be a permanent solution. A paint on barrier won''t change that.