Good morning minggen2011.
Please kindly refer to the ica website that johnnyaz provided
for the criterias eligible for applying for PR in singapore.
Do also check out the singapore police force main website for
the criterias eligible for applying for police officer job here, it
is stated very clearly in the site. they are very strict and firm
on their criterias, so I dont think there will be any alterations
unless otherwise stated.
As for National Service, im not really sure about it, but
I think that they only accept local citizens, and PRs.
However, for more detailed informations, you might want to google
it yourself. To ensure that the information gathered is accurate,
always visit the government's website when you are 'googling'.
Hope my post here is able to assist you.
Have a good day,
Yours sincerely,
tan.