Alternating two forks on a single bicycle — do I need two headsets?
Its a lot of faffing about to swap forks.  They're not really intended for frequent changing.

Best practice in this case would be to obey Rule 12  and to own a second bike set up the way you want it.

Your other option is to buy a light-weight suspension fork, and to make sure it has a lockout.  That gains you the ability to have a rigid, but doesn't give you the weight saving.