SIN Private Room Access
All that matters is your flight out of Singapore - and it doesn't matter what is coded - it must be an SQ flight and a seat in F - but once again I am not 100% certain on.
The other thing worth mentioning is that there is actually 2 star alliance first class lounges at Changi - which is why I'm pretty sure TPR is exclusively for SQ F.
Like I said previously I could be wrong and if I am I hope someone corrects me.