There is no problem (yet) getting the steering head off the rudder post. It is loose on there at present as it rotates a little before the key stops it and so it's able to turn the rudder post. If it were jammed on there I would see no play.
The problem I forsee is trying to get a new key to fit such that there is no circumferential play in there, or very little. Things are going to be worn on the shaft and on the rudder head, methinks.
What I cannot figure is why the designer thought that it would not fret on there? If it is a sliding fit to start with, it must have had a clearance, and even with bigger lock studs, it would fret and so the clearances build with time?