Hi Fabian,
There is no direct support for multiple keys, but it is pretty easy to “trick” ChimeraX into showing multiple keys.  You would create your first key normally, getting it exactly the way you want it to look before creating the next key.  You create the next key with the following Python code:

from chimerax.color_key.model import ColorKeyModel
m = ColorKeyModel(session)

If the above was in a file ending in ‘.py’, you could just use the ‘open’ command to run it and create the key.  I’ve attached a file with that code in it for convenience.  Once you have created the key, then all operations that affects keys (like the ‘key’ command) will affect the new key and leave the original key as is.  If you had the Color Key tool up, it will continue to show the old values.  Just close it and re-open it to show the new values.

--Eric

Eric Pettersen
UCSF Computer Graphics Lab