Thanks for all the answers.

However, I'm still waiting for a response about whether it is safe to apply the patch when a campaign is already in progress?

In other words, is the 56-year death implemented entirely by the .exe or is there a danger that the tendency is somehow embedded in the game-saves? (eg "King X is due to die in T minus 6 years" goes into the saves?)

I'm only up to 1101 in my first post-VI campaign, so restarting won't be too much of a bind, though I'm already enthralled and would rather not have to repeat myself so soon.