Both of them are triggered spells.
The first one you might want to use the Unit - Issue target order event, and detect whether it's a harvest order or not. If yes, you order the unit to stop and display a message for only one player.
As for the second, you could set the vanilla object editor regeneration field to 0 for all buildings, and give an ability based on Item Life Regeneration (Ring of Regen.) to them. Then, use a hashtable or something else in order to keep track of units that have their hp regen disabled so that you may give the spell back to those structures.
EDIT: For the first one, do what Kaijyuu said as it is way better.