Is it possible to convert a boat with wheel steering to a tiller? Impossible? Does it depend on the boat?
Quite possible, and it does indeed depend on the boat.
If you are shopping a boat built in the 70's or 80's, before wheel options became a common option to sell more boats to newbies, a comversion back is quite possible... although not without some work.
If the builder left the original rudderhead in place, it's easy to put a tiller back on after after you clear out the pedistal from the cockpit.
You will then need to put in a new lever control set for the engine and install a new compass.
Like all projects in boat maintenance and upgrades, it just takes Time, Skill, and Money
. All you need is any two of these three!