If you have Colorcurvature's Poser Morph Loader python utility scripts you needn`t worry about breaking expression morphs. You can dial in any pose or morph, export in that state, sculpt, and it will return a layered and separate post transform morph. Makes creating fix and jcm morphs a snap. PM me and I'll send you a copy. Colorcurvature allows sharing of his utility, it was a former mp product. It's GoZ for any app.

There's also another way to do it with subtractive morphing/exporting which is a little more complicated if you don't have PML.

Poser 11 also has convert to post/pre transform morph but I never use it, so I can't speak of it's quirks or specifics... I use PML.