Type "/66change" and a menu will drop down allowing you to choose 12 flower textures, 3 particle sizes, 5 emitting radii or turn the particles on/off.


Caution: If you choose "finalize" in dialog box then the texture, size and radius is fixed.
(even if you type "/66change", dialog box won't drop down)


You can also use the voice command on channel 66, as follows:


Texture:
/66 texture UUID - UUID is the UUID of the texture you want to use.
To obtain that key, find the texture you want to use in your inventory, right click it, and choose 'Copy Asset UUID', and then ctrl+v, it'll get you the desired key.
The command will look like this: '/66 texture c6dbc4b2-918c-b224-8f8d-210b9a07fabf'