Nigs, Jorge and Marc,

thanks for your input. I've now added the following to the variant rules after the previously cited excerpt:

"Therefore, the imperial crown may only change hands during winter turns. As adjustments follow in Diplomacy upon winter SC control changes, it follows that a newly elected Holy Roman Emperor may immediately make use of his newly acquired building privileges."

If anyone can come up with a better phrasing, I'll happily accept suggestions.

Charles