Principle and practice may differ too. As already pointed out, what may be legal may not necessarily safe or wise.
The group A instructor would also need to be aware of restrictions on the use of different types of microlight for aerial work (such as paid instruction) embedded within their permit to fly.
Also if such instruction is for ab initio pilots or NPPL(SSEA) converting to microlight the group A instructor will need to understand the laws, rules and technical subjects relating to NPPL microlight class.
Should a Gp A instructor be seriously intending to go microlight, I'd say firstly, welcome, and secondly, do go and have a word and a flight with a
microlight FIC instructor to find out what they're letting themselves in for... it is a different world and a fun one.
MadamB