Short courses ok.
Long term course is possible to do so but not advisable.
Because when you are serving, Army come first, regardless of what
you are doing part-time. PES E also does not excuse one from
performing orderly duties, in your case maybe duty clerk that
requires you to stay overnight in camp and man the Ops-room with
the other duty personnel (But I like to mentioned orderly duties
will differ from unit to unit).
For example:-
1.) In a month, you might kena duty for 3 or 4 times that you
required you to stay in camp.
2.) Ontop of that you still required to perform your job. In
general, clerk is quite slack but different department different
requirements. Some clerk requires you to do until very late one,
sometimes even overnight. Example, Logistics clerks during
exercise, S1 branch clerks during MOB exercise, etc, etc.
3.) And plus random calls of un-planned things. Like after work
hours job, Unit event, plus alot alot of Sai Kang.
You also must pray that no special army events clash during your
exam period, if not, be prepared not able to take leave during your
exam periods.