Changi doesn't want you to misuse boarding pass (i.e. enter airside without intention to fly). Many people have been arrested for this (entering airside for duty free/escort family, and then try to go back landside without flying).

I wouldn't do it(when you try to exit airside, how to prove you will intend to come back and fly? Or are you misusing the boarding pass by entering first time).

hdogan's alternative plan would work (take a short flight to KUL and return. Wait for friend when you land at SIN)

https://www.cnn.com/travel/article/s...est/index.html.

https://www.straitstimes.com/singapo...changi-airport

https://www.todayonline.com/singapor...changi-airport