Block that generates and spread like moss

Greetings, I'm looking for some help with a custom block procedure, I'm trying to get a custom grass to generate in paths under surface, I want to know if its possible to:

-Only makes it generate when exposed to air

-Spread like moss when bone meal applyed

-Dies or turn into stone when a block with light opacity above 9 is placed on it.

The "dying" when a block is above it its not that dificult to me but the other two are quite complicated