cow level

[Lady Vashj]

So let's say I killed NM Baal, I start playing Hell Act1, just to see how I mannage, then save and exit, start the game in NM, and try to make the cow portal. It can be that by just playing Hell, the leg turns into a "hell leg".

Not in my experience. As long as I keep the legs straight, I can get the NM leg, go back to Normal, and use the Normal leg to get to the cow level while still having the NM leg. Of course, that was pre-1.10.