Yes, when you click "As morph targert", it removes alle existing morphs.
Otherwise they would be baked in the object you want to morph from.

And all existing moprhs would be doubled, when you load it back in Poser.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!