NFC 213 and 215 tags are both capable of permanently locking, so that no new content can be written to them. I think NFC 215 even had the feature of setting up a password-protected write if you want to change it sometimes down the line :)

Oh yeah, I already know how to program the tags, I've done that plenty of times :D

Since the tags themselves are sticky, I'd probably just stick one under a sticker. There probably isn't any difference whether the tag is actually inside the sticker vs just under it. I'd just need a sticker that has an NFC symbol or a "scan here" field so that people know what to do!

Linking to happycow is a great idea! :D I could see something like "find a vegan alternative on happycow" stickers in front of other restaurants