1. I'd like to be able to add additional stock statuses such as 'available in 2-3 days' as well as just 'out of stock'.

I can't see a table or any ability within localisation to add additional stock statuses so i think that owuld be a useful asset.

2. If i can't change a stock status i'd like to be able to edit the text of the stock status for the 'Out of Stock' button that appears here: https://greenwichsketcher.com/gallery/city-of-london/the-flying-horse-finsbury-square. I've created a language override but it does not affect it however many times i flush all the caches. Is this held in js file somewhere?

The language key is the for former. Can't find any others.

I've updated both frontend and admin language keys but it's still showing the original text. Not sure what else is left to flush!

Found it!