After seing Spirit's of the Law video (https://youtu.be/rvJdOKktoMA) I was thinking the only thing remotly similar in the game that can change modes is the trebuchet. I oppened Advanced Genie Editor and 5 minutes later came out with this proof of concept.
We need the ratha to use the normal unit interface but have access to the pack/unpack buttons from the trebuchet. We did something similar with the Sicilian Serjeant so it may be possible.