A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
What happend if I turn Blasted Lands on a province with a region already attached? Can I attach them on an enemy province?
Blasted Lands: After this card turns face-up in one of your provinces, if you are a Scorpion Clan player: Destroy all cards attached to another player's target province and attach this card to it. Rulebook: Provinces cannot attach more than one Region. If there is already a Region on the Province, or it’s otherwise illegal to attach the new Region, discard it immediately.
Regions about to enter play exist briefly in an entering-play area, where their legality is checked.
If you are a Scorpion Clan player, the trait will trigger and you must target another player's province, destroy all cards attached to it, and then attach the Blasted Lands to it.
The trait will trigger before the region is checked for entering play legality.