Never happens on SQ (case in point). The only airline on *A where I have seen this kind of flexibiliy is with LH/UA. UA/AC.
LH with UA especially is very flexible on this.

Even though SQ is in the *A, they not only have an upgrade attitude problem, but also in my opinion a ïndependent attidute problem, frequently disregarding *A traveller needs.

For example, if ýou're flying from KUL-SIN (SQ) connecting to UA SIN-LAX, you CANNOT get boarding passes for UA segments at KUL.
You have to wait at the transfer counter (like I do).

SQ, as far as I know, cannot modify, access, check in any segments on any airline other then their own. Talk about an independent airline attitude. They (ground staff) seem to think, IMHO, that SQ is the only airline around.