If you want to take out 1/8th of a MM, it can be done manually by sanding it .
If you want to take out more than that , it might need re-tapering on a taper machine.
The joint protector might need to be center drilled and maybe spur driver slot/slots cut so it can be turned steadily on a taper machine .
That's assuming it is straight or only had a slight wobble that can be taken out with a 1/4 of a MM cut.
I have a laminated Lambros shaft here for re-tip and cleaning.
It does have that gradual "pro-taper". 12.5MM tip and goes up to 13MM in 14.5" ( middle of the shaft ). Nice gradual taper preferred by most players these days. Fairly easy to duplicate.
Keep in mind this is the laminated one. I did not caliper a regular ML shaft I had here one time.
Or you can just send it out to ML.