1 flight coupon for 2 flight segment
 

I apologize for cross-posting, but need some feedback from UA (esp those who work at check-in) on this matter.

I got 1 flight coupon as part of my CRWSTAR (RTW ticket) for SFO-NYC (JFK). I need to get to LGA instead and I believe there isn't a direct flight from SFO. Will there be a problem if I make reservations for a flight that involves 2 flight segment (SFO-ORD,ORD-LGA), but I have 1 flight coupon.

FYI, my ticket is issued with SQ, and if SQ makes the relevant reservations and confirms it, will UA back out of it and say no go later at check-in.

NO. One flight coupon will work.

no problem, as long as:
* this is not the first part of your rtw-ticket (changements are not allowed for the first segments including the first flight to another continent)
* the new total of segments doesn't exceed the max segments allowed with your rtw ticket
* the added miles of the two segments doesn't put you over the total miles allowed
* you are willing to pay for the changements of your itinerary (the rules depend on the country/continent wre you bought your rtw ticket)

And even then, they might not charge you, especially if you try to do this day of departure, and especially if you're willing to fly standby to the co-terminal (LGA instead of JFK.) (Remember that UA's free same day standby rule for US domestic travel always allows you to opt for a different, legal routing.) The very-low-tech workaround of United's is to print a "gate pass," also known as a "reissued flight coupon" for the connecting segment, and to use your current (SFO-JFK) flight coupon for the first segment. Alternatively, they could go through the hassle of re-issuing the ticket, but that will definitely incur all of the tests that Rudi mentioned.