AuntBee,
I have a few thoughts
1. It should be easy for you to get a name tag. Post a topic on this forum asking for somebody to scan in a copy of theirs and you can print one out
2. I've seen may people video tape the conventions before. Just find a nice place to sit where the videocamera is out of the way, put it on a tripod and go to town. Nobody is going to ask any questions and if they do...
3. Just write on your name tag that you are from a congregation far far away (or ditch the nametag and just say you are on vacation!). Anyway, I'm sure nobody is going to take notice of you as long as you dress to fit in.
Some other tips: Turn the tape recorder on and off after each talk and don't record the songs. A mini recorder is great because it will create a separate audio file for each clip you take, that way you don't have to worry about breaking them all up into individual files. If the convention is being broadcast on an am/fm reciever all you would need to do is turn on a small radio and use a 1/8" audio cable to connect the radio output (headphone jack) into your digital recorder (microphone jack). That should provide a perfectly clear recording (just make sure you set the volume levels at a good setting, not to loud not to soft). Bring lots of extra batteries ;)