It’s not possible, there are several files that need to be changed to be able to add more.
For example, we only have 9 mastery enumerations:
The “mastertable” file only has support for 9 control panes (these show the mastery and all the skills once you select a mastery)
But we have 10 slots for skill trees in the character files…
though it doesn’t matter because without the enumerations or classtables for masteries past the 9th, you won’t see them properly.
Beg to crate so we can have infinite masteries! TQ + GD + NCFF!