Why mess with the screw at all. Well, you don’t want the screw to vibrate out and guess where it will go? Right into one of the cylinders forcing you to remove the head.
I personally don’t like the idea of beating the small throttle, or choke shaft screw with anything as it might bend the shaft. Especially since most shafts are not available anymore.
Back in the day we had a tool that you squeezed and it mushroomed the screw for you. Unfortunately that tool is no longer available. Although I admit I have looked that for the tool too hard.
Simply apply some red, or blue thread locktite to the threads. That will keep it from vibrating loose.
What do you do when you need to remove a screw that has a mushroomed threaded end?
I use a Dremel tool to grind the screw down to the shaft. That almost always allows the screw to come out easily.
If you don’t know how to use a drill and tap, or don’t have the tools, then I suggest not taking the valves out.