In vanilla Vintage Story, there is a specific crafting recipe you can use to add a label to a crate. You cannot add a label to an already placed crate. You would have to break the crate to pick it up, and then craft the "labeled crate". 

Well, now you have an option to just slap the label on whenever you feel like it. 

Batteries included:

• Makes a satisfying thump when you attach the label
• A new block interaction help entry showing you how to do it

I have added a lot of checks to prevent blocking normal crate functionality. You can add a crate only if you are holding a parchment, are looking at a crate that doesn't have parchments inside, and doesn't have a label yet.