Could I use an RF antenna to write information to the tag's memory chip? I am thinking in terms of labels for packaged goods.
You would need to use passive ultrahigh-frequency (UHF) RFID tags that support writing to user memory. This is part of the Electronic Product Code (EPC) specification, of course, but tags aren't required to be read-write-capable. It is possible to have UHF tags that are preprogrammed with an EPC and cannot be written to.
When you buy a passive UHF RFID reader, it will come with a program that will allow you to write data to tags. Every reader is different, but there are a set of uniform commands that allow you to write data to a tag's user memory. The device does this remotely by emitting radio waves that first indicate the command to the tag and then send that information to be stored in user memory. There are several user memory blocks, so when setting up the reader to write to the tags, you will need to indicate which memory block you wish to write data to.
I hope this answers your question, and I look forward to seeing you at RFID Journal LIVE! in May.
—Mark Roberti, Founder and Editor, RFID Journal