I think it would be safer to do something like this:
1. Yankee concedes and Blair is inaugurated
2. At some point Blair appoints Yankee Vice President (elected VP stepping down)
3. After two months since taking office, Blair resigns, making Yankee President
I know, it sounds like more complications, but I prefer doing this rather than have another legal challenge, delaying everything. We can always amend the constitution later.
I agree with the caution expressed by the ever wise GM.
I PM Blair expressing my support for a slight variation of this arrangement as communicated to me in his most recent PM on the matter.