I don’t recommend ever taking off your harness on a big wall.
My best big wall harness designs had leg loops that were easily detachable in the back. Then you *could* remove the leg loops but still have the full strength waist part of the harness, assuming your harness is designed that way.
Removing a harness on a big wall is not a standard practice. Ok, sometimes i did it when on a massive ledge, for a short time. But even then, with extreme caution. You never know what will happen.
Of important note, all portaledges are designed for comfort and convenience, none have ever been load rated and are NOT safety systems, like a harness. So replacing your harness With a sling is the same as climbing with just a sling. You never know what could happen on a wall, when you read accident reports in the AAJ journals, you will note that most accidents are the result of a sequence of assumptions, not just one thing. Take care.