As the awning would be fixed to common property AND would affect the appearance of the building, a special resolution by-law would be required.
That by-law could (and should) specify the design and colour of the awning, and the capability of the installer, as well as ascribing future responsibility for the awning, plus the common property to which it was attached, to the lot owner.
Your committee needs to have a discussion about what designs would work and then set a benchmark. If the lot owner refuses to be limited in this way, you simply advise the owners corporation not to give the necessary approvals.
As for setting a precedent, think of it as setting a benchmark for future installations.