I'm sure even a crusty old SSM would not be expected to know every person who had medals, or what they were. I'm also sure any 'reasonable' excuse would be accepted for not wearing them (being remounted). However, if I heard "Tommorrow's parade is in DEU with medals" I would consider it a direct order. My honesty, to myself, would say "Yes, I have them". My integrity would say "Wear them as directed". That's where I'm coming from on that.
I understand why it would be wasteful for some to wear the decorations awarded to them. They would only be covered up by the barrack room lawyer shingle that’s hanging around their neck anyway.
Not saying this about you, just saying.
Anyway, I'm not going to debate the legal meaning of 'should, will and shall'. I deal enough with that one at work.