I don’t pretend to speak for anyone else, but for me, most complete lights I buy off-the-rack, I leave as-is. Call it laziness. If I don’t like something about the light (blinkies, the UI, etc.), I just don’t buy it, period. Lots of lights I just walked away from, because a review or comment pointed out some annoyance that I really didn’t want to deal with.
Otherwise, some lights I’ll buy only for their value as hosts, and strip them down to parts as soon as I get them. The UF F13, ferinstance. Typische annoying H/M/L/strobe/SOS, but acto an OldLumens vid someone posted, it looked quite moddable, so I got a few. Wellp, 22mm driver instead of 20mm, but doable. C8s? Damn, I’ve got an army of C8s, ready’n’waiting for whatever LED, driver, etc., that I’d want to throw into it. Same with lots of ’502s and a few ’501s.
I agree that lights shouldn’t be epoxied shut (not unless the mfr has a no-questions-asked warranty in case the slightest thing goes wrong). But using Fujik instead of AS5 (or nothing) shouldn’t get them unnecessary razzing.
Once you open it up, though, don’t count on a warranty. What mfr in its right mind would cover a “hotrodded” light? “You break it, you bought it.”
Still, it’s really nice to be able to mod a light and not leave it bone-stock, if that’s what you want to do. As long as you’re not counting on a warranty, sure, make it mod-friendly.