Can only shim clutch type diffs, most basic Nissan use Viscous diffs.
Aslyls S14 Racecar has been on a welded GTR diff without problems. GTR is easy as you can weld the clutch plates so if the weld fails it just goes back to normal GTR LSD, If you weld other types you need to weld the spider gears and when they break shit goes everywhere.