There is no way you will be able to convince them to book you with SQ. Sorry for being a party pooper. There are plenty of flights among LX LH and OS. If you ask me I would rank OS and LX pretty much the same and LH a bit lower. I think the food might be a bit better with OS. Last as someone has said the days have gone when they used to rebook you in a higher fare class. Only if it’s a last minute rebooking this might happened. I remember I had some lovely rebookings with LH T fare to Y. Lots of miles.