Having watched our PB install nicheless lights in our new build, it seems like adding them to a remodel would be relatively straightforward. I'm assuming they'd use a core saw/bit of some sort to drill through the shell, run a sleeve, bond the sleeve to the shell, and then run conduit from the light back to your control panel. As mentioned above, the complexity and cost will depend on access to the back side of the shell as well as how the wiring can be routed to the control panel (i.e. does it have to run under existing decking/structures).