You can always prepare for any other exams if you are passionate and hard working. Since both the exams CDS and CSE are conducted by UPSC, the syllabus are most likely same and you have to do less hard work than the other aspirants.

But the time for preparation is also a thing. Generally, army officers are only given 60 days of leave in a year and only 20 days of casual leave excluding sick leaves.

There will be nothing like to give someone leave for the preparation of the examination.