Use a small round grinding bit in a Dremel to remove the molded-in trim rings... glue a piece of sheet styrene onto the back (inside) of the rear panel with liquid cement... fill in the existing holes with discs cut from sheet styrene glued to the new "backer plate"... add Bondo... sand the rear panel smooth... drill new holes for lights in the correct size and location. Use rings cut from aluminum tube for the bezels.
Another way to go: Use a Dremel to remove the entire existing rear panel, make a new one of sheet styrene, drill for lights, glue in place, Bondo, sand, etc.
A bit of work, but not "major surgery" at all.
An even easier way to go: fill in existing holes, smooth the back panel, put BMF on the back sides of the light lenses... then just glue the kit lenses and new aluminum tube bezels in place on the surface using clear acrylic as your "glue." No need to even drill new holes. Super simple.