Dependable on NS units, CSM and RSM.
If you're in training phase, e.g. OJT, your haircut will be still as short as in post-BMT.
If you've posted to a permanent unit, they generally allow hairstyles, provided still must be short, neat and tidy. In other words, just trim your hair just as in primary school.
NSmen/ Reservists generally can keep hairstyles, provided must still be short, neat and tidy.
1. Acceptable haircut for male.
Moustaches are permitted. If a moustache is kept, it has to be kept neatly trimmed and of moderate length. No portion is to fall below a line parallel with the bottom of the upper lip or extend sideways beyond a vertical line drawn upward from the corner of the mouth.