Originally Posted by Zorak

I think he just mis-typed, pretty sure flyerCO knows the rules

RE: OP's situation, just to clarify, it's not that a 4+ hr layover creates a broken fare, it's more that, the only way to create a 4+ hr layover on a domestic ticket is with a broken fare. You can also have a broken fare even with connections less than 4 hours and you'd have to look at your fare construction to know, but given the 4+ hr layover we know without looking.

Given the fare break, for SDC purposes you didn't really have one ticket from LAX-DTW-LGA-MHT; you had two tickets, one from LAX-DTW and a second one from DTW-LGA-MHT. SDC does not let you change origin and destination, or change a connection into a nonstop. So strictly by the rules you could SDC to a different LAX-DTW flight, or add a connection LAX-XXX-DTW. And on the second "half" you could SDC DTW-LGA-MHT into DTW-YYY-MHT.