In standard form x^2(d^2y/dx^2)+x(dy/dx)+(x^2-n^2)y=0 last term is (x^2-n^2). How to tackle the problem if instead of minus sign we have positive sign. i.e: (x^2+n^2)
I guess either you are giving incorrect information about the problem or may be I understood it wrong. Standard form should be (x^2-n^2) or (x^2-n(n+1)). And as per the standard definition n can be complex and has the same result independent of the sign of n if n is real.
I think you should look for the original steps involved in obtaining the standard solution and from there you can get an idea respective to your problem.