just go ns.sg, click apply exit perm after you finish your Uni.
But it put down as staying overseas.
There are people who stay overseas and never come back to
Singapore, And they dont even have a house in Singapore. So you can
put down as working overseas or extension of school or whatever.
Nobody bothers one.
The idea of exit perm is to do a headcount on how many people
are deployable when needed or during a mock call up.
It is not uncommon that people dont come back to singapore after
studying overseas. Gendaken is one. Ask him