Recently I have seen two firearms up for sale where the owner customized the firearm and turned it into something only a mother could love. One was a Taurus 1911 with a retail price of about $600 and after all the customization they wanted $850 and the gun was orange and black. I would never pay 30% more than a gun was worth new unless there was something super special about the custom work which was done, but making it orange lowered the value IMO as opposed to raising the value. Another was a Glock with a cerakoted frame which was OD Green. It wasn’t bad, but why would I want that? Another one was a Glock with $175 worth of custom grip modifications which to me look like someone took a hot paperclip and stippled the grip. There were other modifications, but why would I want a $550 used Glock when I can get a used Gen 3 for $400-450 all day long.
If you are going to modify the firearm there are a couple of considerations. First and foremost is the modification just for you. If so they gopher it. If you are doing the modification with aspirations to eventually sell the firearm and recoup the cost of the modification be aware the chances of this happening are slim to none. So if you stipple the grip on a Glock, know it is lowering the value to many. If however you were adding night sights to the Glock you would potentially increase the value. You can change grips on some guns and other things, but save the original for when someone like me walks up and says that’s good, but I’d prefer original.