As far as I can tell, MPS doesn't support in-line protected code regions for manual editing in MPS. This feature is supported in Xpand and OMG's MOF MTL. (http://www.openarchitectureware.org/pub/documentation/4.3.1/html/contents/core_reference.html)
Is there any way I can similarly combine manually written code with generated code in MPS? The reason I need to do this is while in the process of migrating existing code into MPS, it makes it much more feasible for me to move to MPS iteratively.