Both Dunlop and Schaller straplock pins use "small head" screws that fit into the recessed cavity of the straplock. I've yet to find a guitar/bass where the original strap pin screw will fit the straplock cavity. Unless you own a mint historic collectable instrument, you're not going to adversely affect resale value by fitting straplocks. In fact, having straplocks fitted would be regarded as a benefit by the average buyer. For one, it shows that you care about your instrument and that it hasn't been dropped
In most cases the straplock screw fits the original hole, although sometimes it's a tight fit, so a properly fitting screwdriver is essential. You can also make it easier to screw the slightly heavier gauge straplock screw into the hardwood body by lubricating the screw with wax or soap (non liquid) first.
All my basses have Dunlop straplocks fitted, and I've kept all the original strap pins, so if a potential buyer gets hung up on having the original strap pins, I can just refit them before sale. Too easy.