You can ask them but SQ doesn't have a good track record of complying with these types of requests. However it doesn't hurt to ask. 17 hours does sound painful. I'd ask multiple times (to different people of course).

It SQ modifies your ticket you will not have the rest of your journey cancelled. Defeats the purpose of getting an earlier flight. Your ticket will get cancelled only if you don't board the SIN-DEL flight you're supposed to (original or modified) not if the airlines makes modifications to your ticket.

They should do it without charge unless there is a change of class say from Y to J. That's the general policy all the times I've done this (a few times with US based airlines and once with AI). The same should apply to SQ.