Hi, Henry. Re: fixing a hak for easier bathroom breaks:
Theoretically, yes, it can be done as there is a center front seam.
I do not recommend velcro--its a personal issue, I HATE the noise.
What might be very discreet and easy is snap tape. This is used on the inner leg seams of toddler's trousers for easy diaper changing. Its 2 matching lengths of a soft cotton twill tape with snaps attached at intervals. I have used snap tape to keep my gi tops closed and imagine that it would do what you suggest at the center front seam of the hak.
What I do, as a person of the female pursuasion, is
1. replace the drawstring in the pants with elastic
2. tie my hak in such a way that the back half can be dropped without undoing the front half
This allows a convenient, fast sitdown and would work for men too if they don't mind sitting instead of standing.
hope nobody's offended, I'm a nurse by profession....