It's impossible to have infinite durability with a save editor. You can keep setting it to the maximum (of note here this will not do that -- you'll need to use the web-based editor to get the maximum and this goes significantly less high) which makes them last a really long time, but if you want them to be infinite you'll need to use this LayeredFS mod:
https://gamebanana.com/gamefiles/7369
I hear SX OS has a lot of issues with LayeredFS as the code they stole was from a really old Atmosphere (apparently they aren't updating that part of the code) so it may have problems, but I think with this sort of thing it should work just fine.
The game is definitely a lot more fun when you don't have to think about weapon durability anymore. This is really how the game should have been by default. They should have done something more like this for normal mode and only had durability in hard mode IMO. For me it didn't work just to use the save editors anyway because I still had to worry about durability. Quite a lot less in comparison (you can still set it insanely high even with this) but you know it's going down and the weapon can eventually break. What you may want to do though is combine the two things. You can edit in properties using a save editor and set their values (so +damage and then add 10 for instance.) So you can pick your favorite weapon, add on a damage bonus that makes it increase to the same damage as later weapons, and just run around always using the same thing instead of having to switch around all the time. (Only one property on each weapon though sadly. You can't, for example, give something increased crits, extra damage, and increased guardian damage. It's one only.)
BTW, if you're messing with LayeredFS mods, you may want to try this just for the sheer fun of it:
https://gamebanana.com/skins/164945
https://gamebanana.com/skins/165761
https://gamebanana.com/skins/167565
(The DLC Wave 4 may actually overwrite all the DLC Wave 3 files, but I'm not sure, so I'd say just do them in that order, hit overwrite all, and you'll be fine.) Obviously this is entirely optional and, in fact, unrelated, but fun anyway.