The other problem with changing aperture while shooting is that you're touching the camera and introducing shake.
Cine lenses, such as this
, are the way to go if changing aperture while recording is something you want to do on a regular basis. Get a rig with both a follow focus and an aperture wheel. Or just use your fingers on the geared aperture ring. Likely far less shake introduced than using buttons on the camera and much faster to boot.