Is it possible to add qualities like 'Durable' to armor types that normally don't have it?

And what kind of skill/time/price would be involved to that? To e.g. make a Lacquered Armor also Durable.

Same with adding other qualities to other items (armor/weapons)...

Yes - it's a refine action, using smithing. See the skills chapter.

There is also this Earth opportunity on page 329: add the Durable quality to an armor you are restoring. Very useful, given how easy it is for armors to get damaged with bogus critical hits (at least in RAW).