When switching from a stair rail to a handrail, follow local building codes. The biggest mistake people will make is the top of the horizontal landing handrail, and the top height of the stairway handrail might be different after you've switched them. You want to make sure that doesn't happen.
When home inspectors measure stairwells, they check three things: height, graspability, and baluster spacing. If you violate those you will be fined and it will be harder for you to sell y9our home.