How to prevent further oxidation and stabilize condition of old copper coins ?

Hello,
I have some millennium-old coins in a smooth stabilized state

DH#16.212

.

And I have others that have a grainy oxidized appearance.

DH#16.210

DH#16.211

How to stabilize this oxidation?
- coat them with olive oil?
- dip them in a bath of sodium bicarbonate?
- another gentle method.
or simply do nothing because if they have lasted a millennium, they will surely outlive me :)

Subsidiary question: Is my classification DH#16.210, DH#16.211, DH#16.212 correct?

N#34504

I have a couple of UNC coppers I received in the 1970s that are lacquered (simple organic varnish). Today, more than 50 years later, they look as if just out of mint. 

If they are really a 1000 years old they should be stable, otherwise they would have been long gone (bronze disease).

Just check if they are of the hard type green patina and not the brittle kind that eats your material away (if the case remove it and keep it neutral or slightly basic).

Have you looked at Fluid Film?                                      

There are several varieties, A, AS-R and NAS.
They are not available in France except maybe through Amazon.
And I would like to try a method approved by some collectors of ancient copper coins.

I have few times used WD-40 for Chinese cash coins with no negative reactions.