It may depend upon your camera. Some have an easier way to manually adjust shutter rate on the fly.One of my all time favorite videos. Led me down a rabbit hole of trying to figure out a way to make the capture rate adjustable when filming. Never did find a way.
Yeah, there are some professional cameras that allow this and some technical ones as well. Didn't ever find a way in a consumer or prosumer camera.It may depend upon your camera. Some have an easier way to manually adjust shutter rate on the fly.