Add support for whitelisting which blocks are allowed to regrow.
Create an IMC API for allowing mods to whitelist their decorative blocks.

Yes! Cobblegen sheep! Glassgen sheep! CAKEGEN SHEEP! cackles insanely Umm...
Alternatively or additionally, a slow breeding/production cycle like the Chickens mod. Whitelist diamond sheep, but set them to take an hour to regrow a shard.