If the truck is stopped, the rear part of the tcase should be stopped, too. If the tranny is in P, the input shaft stuff should be locked stopped, too. No grinding is then posssible, but it may be hard to get the tcase shifter to go into 4lo due to gear engagement misalignment. A slight roll should line it up. If the engine is stopped, it should shift into lo range or any position fairly easy, if the truck is allowed to roll slightly. The shift from 4hi to 4hiL is only a syncro engagement.

I think there's a special goo in the tcase for the activetrac, but I'm not sure. Seem to remember that the wrong goo will cause problems. May be confusing it with a quadratrac too, so beware this particular advice. I was wrong once, and it could happen again...