The enrichener knob is plastic and can sometimes break. \ If you just want to swap to another style for looks, there is no set screw to remove it as it is molded onto the pull rod.
So it'll either have to be broken or cut off.
Several options can be had to replace the knob. It can be done without removing the carb from the bike.

You can go to your local home improvement store and purchase a nice looking kitchen drawer pull knob. ¹⁾
Enlarge the hole with a drill bit to rod and then glue it in place with epoxy.

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This one was done with a “Mooneyes” Deco Dash knob p/n SPC8425 $8.00.
The ID of the knob was originally too small so it was drilled out to fit.
The tools below were used for the replacement.

Before you remove the knob scribe the choke rod where it meets the knob with a nail.
This is to make sure the new knob ends up in the same place when it's pushed all the way in.
Next, a pair of metal shears were used to chip away at the plastic. Don't be in a hurry and don't tug, bend or pull on it. Just cut small pieces.
It takes a while but it will come off. Make sure to wear eye protection since the plastic will fly all over the garage when cutting on it.

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If the ID of the new knob is too small, you'll need to drill the hole out larger to go over the stud.
Start with a small bit and work your way up with larger bits until it fits the rod.
Note: Drilling into plastic creates heat which melts the ID larger than the drill bit.
So using a bit exact the exact size of the rod may result in a hole that's too big.

After drilling, it was found that the hole wasn't quite deep enough.
So a drill bit was taped off to mark the correct depth to make and the knob was re-drilled until it met the tape line.
Then the knob was installed on the rod with thread sealer (nail polish in this instance) and the set screw tightened up.

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