OK maybe we should create a wiki entry or something because this questions seems to pop up fairly often...
Since LX has no spare aircraft in case of mx, they sometimes use WK (Edelweiss) aircraft to operate on their routes; if that happens, nothing regarding mileage accrual will change!
Btw, the OP is lucky, SWISS used to put A321 on this flight to TLV, so an Edelweiss A330 is much better!