I have been trying to find any canon-based answer to the question if and how regenerations could be stolen from a Timelord.
We know that the regular 12 CAN be added to because it happened to both The Master and The Doctor by now.
In "Let's kill Hitler" River proved that it is possible to choose to share regeneration energy. Some reading up on the old series gave me this:
Time Lords were also said to have "packets" of regeneration energy in their bodies, one for each life. These packets could be physically removed from a Time Lord's body, essentially robbing them of their regenerations.(TARDIS Data Core)
But is there any Canon-based information if Regenerations can be transferred from one Timelord to another which I missed? Can this transfer be forced?
Addendum: What is making me struggle to fully wrap my head around this: River clearly did not remove anything physically... but she healed, she didn't actually transfer the regeneration-ability. A Physical transfer of "packets" seems a logical possibility. A pure energy-transfer-addition seems possible (see Day of the Doctor). But could Timelord A force Timelord B to "transfer" regenerations purely energetically? ...I may be overthinking this...