I'm visualizing this, and I don't like what I see. Yes, CDA, he's talking about a door/grill, inside the exit enclosure, that would be placed at a landing, to keep people from going up the stair, into the part of the enclosure serving the top 4 floors.
Handicapped issues aside, I don't know how this could be reconciled with door swings adjacent to risers and landings.
But let's just play along, and say the landing was HUGE, and a door could be placed such that it was adequately separated from stair risers, and did not reduce a required dimension of the landing.
Edit: Everything I wrote earlier has been deleted past this point, replaced with:
Unless this building complies with the High Rise provisions of 403, you can't do this. Section 1008.1.8.7, Stairway Doors, prohibits these doors from being locked on stair side.
Comply with 403, or abandon all hope of this ill-conceived plan.