Now ... suppose someone wants to mess with the UK ... Now, iirc, the catechism allows for 'emergency baptisms' to be carried out by anyone, not ust a Catholic priest. So, you somehow get access to little Georgie and ... baptise him into the Catholic church!
There, Done! Can never inherit the crown! Deconvert? Rebaptise as an Anglican? Not gonna work. Once a Catholic and you're out to the succession for good.
Muslim? Hindu? Satanist? Those we can work around ... but not Catholic.