My experiences with SQ tend to confirm that they are not flexible, unless (of course) you hold an F ticket. Perhaps Ive been unlucky?
Generalizing about any group of people(s) is a risky probabilistic endevour, unless you have a large enough pool of experiences to make your sample a valid one. With SQ agents, I believe I do. In any event, I will say that Ive actually encountered one case of an SQ agent that surprised me for her flexibility (alas, it was not @Changi but at the SQ PEK office).
All my other experiences with SQ agents & phone reservations have been that they have trouble handling anything thats not absolutely plain vanilla. For all other things that require going the extra-mile, phone call, looking up fare rules, etc. (what one would call "real" customer service), the standard answer from an SQ agent is "sorry Sir, thats not possible". PPS, C class, loyalty to SQ, and all other things that are considered at other carriers go un-noticed.
Im not a Solitaire (only a PPS member), so I cant speak for the treatment they get, but my repeated questions to those that have such status usually yield the same response " no special treatment ".
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Gaucho100K