Explain your idea

Rather than extending BushBlock and having and EnumProperty for the age of the crop, HempBlock could extend CropBlock and override the parts regarding the age property. To distinguish the top from the bottom a BlockState property could be added, like it's done for Thermal Cultivation.
This change will allow better compatibility with mods that expect cultivable crops to extends CropBlock. For instance, Harvest with ease does not work with hemp crops currently (right-clicking does not harvest).

We can't do that midway through a version, because Crop blocks have completely different properties.

I understand, meanwhile I thank you for considering my suggestion and I hope that in a future release it will be added!
Thanks again!