Update:
Moses Scott McComas married Barbara Stream 7 Jul 1829 in Greene County, Ohio.
Moses Scott married Susannah Skirvin 22 Aug 1831 in Campbell County, Kentucky. (That is about an hour south of Greene County, Ohio in modern travel)
From 1840 on, Moses & Susannah Scott and family are in Grant, County, Kentucky (about another 45 minutes south) They use the name Scott until 1860. That happens to be the time Moses died.
Susannah and family are listed twice in the 1860 census, once under Scott and once under McComas. The children use the names Moses McComas and Susannah Skirvin from then on. The only exception is a death certificate that lists Moses McComas and Mary James......I believe this to be a case of the informant didn't know the answer to the question.
To me this name change, of Moses Scott McComas to Moses Scott seems like a case of not wanting to be found by your first family of in-laws. Of course, we will never really know the real reason of the name change but I am confident in the research that Moses Scott McComas and Moses Scott are indeed the same person.
This is one of the most unusually difficult genealogy tasks I have come across