I like to think of "warranty" and "service" as two different things.
Your warranty could be blown, but they would still service the knife. Servicing as far as sharpening, replacing washers, thumb studs, lanyards, pins, screws, etc... Warranty as in, there is a lock bar issue or maybe the blade cracks around the thumb stud... you are S.O.L. on stuff like that.
I just sent a Sebenza 25 that was "nuked" in for spa service and they sharpened and tuned it no problems at all. Charged me for washers, sharpened for free. My washers were pinched though, so would have charged no matter what. Got it back on this past Friday. No worries. "Nuked" is electro-anodizing and stone washing. The stone washing I thought would have been the deal breaker as that actually puts tiny little scratches into the titanium, but they took care of me.
Electro-anodizing under normal circumstances does not hurt the titanium, and something done this way can be undone easily, all without hurting your titanium. I think the important part is to make sure the person you have do the work is reputable and not an idiot who will just let the scale sit in the acid too long because that will ruin your titanium scale. I have a Large 21 right now that is kind of blurple, but I could restore it back to factory if I wanted to with stripping the ano and bead blasting the scales.
I have one knife, a modded Mayo Sebenza that they are not very fond of and I would not even send it in for service. It has holes drilled through it by Tom Mayo, which eh, you either love it or hate it.. its ok. Not for everyone. I'm kinda on the fence about them, but it was more of just wanting one of the rare Sebenza mods by a legend. The other would be the Vallotton mods, but those are even rarer.
Tim Reeve kinda mentioned recently some changes are coming. I think they are starting to take a stronger stance against mods. Just my thinking. Only way to find out though is just going to be waiting until they make their announcement.
But as of now, they took care of my nuked 25 and I can't say enough about this company. They really take good care of us and their knives.