.....just weighing up how much trouble this may create for myself with the better half 
Just do what they do and say, they have been in the wardrobe for ages, your mum gave you them or you got them in a sale at a ridiculous price.
Or if she's anything like my Mrs just put them on and she probably won't notice

I changed from an RCD510 to the RNS510 and she never noticed a thing. Put the Nav on and when the directions were spoken out she said "I've never heard that before".........
"I've just never used it before dear!!" 