Join Date: May 2004
Location: SIN (LEJ once a year)
Programs: SQ, LH, BA, IHG Diamond AMB, HH Gold, SLH Indulged, Accor Gold, Hyatt Discoverist
Posts: 8,815
The SDFC concept is not offered nor honored by SQ (e.g. in case you think it should be granted by virtue of you booking via UA). It is a very US carrier thing (nice, don't get me wrong) and UA offers it for their own operated flights only. Unless your fare conditions allow for free changes that is.
You can ask SQ transfer desk of course and may get lucky, no harm done, but don't be put off if they say no or tell you about some change / up fare fee or so.