Is it possible to create a rocket with a variable blast diameter to achieve different levels of torque and power similar to a geared transmission?

I suppose the best analogy I have is the difference in power between a garden hose normally and when you plug it with your thumb, creating more pressure.

Would it be possible to have a rocket launch with maximum diameter, and slowly close up like a camera shutter to gain speed once in the air? Perhaps this shudder would be angled like a funnel to direct the blast easier. All the rockets I see have a fixed diameter and it just makes me curious.

(Asked Bharath)

Experts in the field are requested to answer via comments