Not being funny, but if the slit is big enough to cause a bulge, then replace..... if bodging, use some emery paper for a TEMP repair.... most slits that don't cause a bulge are OK, but any that do means your tyre is goosed !!!
Stelvios OK - yep........ but I ride Pro Race..............
Puncture protection is rubbish....it leads to a slow and heavy tyre !!! Been there..done it......