Not really possible to DIRECTLY have a reaction transform dwarves into stuff--just like it's not DIRECTLY possible to have an elven citizen. But you can get Cacame or an equiviant to migrate to your fortress, and you can find a workaround to transform dwarves with reactions.
1. Create a new inorganic.
2. Give it a boiling point below room temperature.
3. Give it a [SYNDROME] which is [SYN_INHALED]. This syndrome should have [CE_BODY_TRANSFORMATION:PROB:100:START:0:END:1][CE:CREATURE:DWARF:MALE] or whatever,
4. Create a custom reaction that creates 1 BOULDER:NONE of the above material.
5. Add the reaction to the MOUNTAIN entity's list of permitted reactions.
6. Generate a new world.
If I'm understanding this right, what you did was create an item that can be inhaled, or was inhaled at creation. Then that item transformed the creature into itself. And the create 1 boulder:none reaction, whats that do, remove any materials needed? Or remove the item it generates.
So Mountain entity is for dwarves right? I'd have to create 2 regeneration chambers then, one for males and females?