I'll give you MY answer with the understanding that I don't officially speak for Predator Corp.
or to their definitions of terms given in their warranty.
All Gen2 Predator shafts built by Predator already have a phenolic insert or plug installed.
If the factory-shaft being built is to be built for a 'big pin', the phen. plug is drilled/tapped for that thread.
If the shaft is to be used on a 'small pin' cue, ie, 14, 18 or Uni, the insert is set into the phen. plug.
When a brass insert is removed, the hole is already too big to accept the big pin.
Predator supplies me with the proper plugs for this type of conversion as well as the plugs used at the factory.
More directly to your question, I would think that it depends on who does the work and even then would be
evaluated on a case by case basis.
Both types of phen. plugs require special tooling for installation.
If not installed correctly, damage to the shaft could occur.
I believe that most competent C-Tecs could perform this task if instructed and they had the tooling.
Would Predator warranty that work? IMO, probably not but that's why I stated 'case by case'.
My work on Predator cues & shafts is authorized by Predator.
KJ