I don't use Foursquare myself, so I'm not too familiar with it, but looking at their developer documentation (https://developer.foursquare.com/resources/client#nfc)it looks like Foursquare NFC tags for Android are just URLs that contain an ID at the end (don't know if it's the same for N9, wouldn't make much sense if it was different for different phones though!). If you know the venue ID you could simply type it by hand in the URL.

Of course typing complicated IDs by hand is boring, and perhaps the Foursquare API could be used to ease the process. But I haven't really familiarized myself with that yet.


As for locking tags read-only, that would indeed be nice. But it requires sending tag-specific commands, something which the N9 NFC API doesn't allow even in PR1.2. So unless that is fixed in PR1.3, this will be impossible.