If there is no written procedure for a particular activity that you regularly do then why not raise a Quality Failure Report against the MM and let the QA dept sort it out. After about 10 their enthusiasm for chasing after you for not providing the reference may wane a little! But seriously, AWN3 obviously can't cater for every eventuality, most of the time its up to the licensed engineer concerned to make the final judgement. Our company has very clear procedures as to what people can and can't do within it which helps enormously. I've found, in the past, the only way to get any action from QA depts is to put any queries in writing. Food for thought?
PS I don't work on large aircraft - so what is a shear deck?