Not that I would be encouraging people to circumvent paying taxes which we all know are there for our benefit (??? )
Take the new parts out of their packaging
Wrap them in oily paper towel, put in a plastic bag secured with rubber bands.
Use old dirty oil and perhaps some newspaper.
At the border, they are your riding spares because as they all know these old bikes are very frail & break down all the time ..
Put your new bars on the bike & the old ones in the pannier which is there in case it falls off the stand & bends the bars so you can ride home legally .