What you'll need:
-If you're using a non-Sony device (I'll be using my Galaxy Nexus), you will first need to install the Sony Liveware manager and Xperia SmartTags applications from the Play Store.
-Sony users and non-Sony users alike will have to install NFC Tag Writer and Reader.
-A suitable NFC tag. I used these Mifare Classic 1K tags which came in a pack of 5 for £6.
Thanks go to Alastair Aitchison and his reader James for this discovery!
1) Open NFC Tag Writer and Reader. Select the 'write' option and then 'reset tag'. This will clear the tag of any data that already exists on it.
2) Go back to the NFC Tag writer menu and select 'write' again. This time you'll need to select the 'URL' option. Get rid of the http://www. and instead paste in one of the URLs that I've listed below. Select the write option to write the data to your NFC tag.
To make your tag into a 'Car' tag, paste this URL: semc://liveware/A1/1/NT1/1/smarttags1
To make your tag into a 'Home' tag, paste this URL: semc://liveware/A1/1/NT1/2/smarttags1
To make your tag into a 'Bedroom' tag, paste this URL: semc://liveware/A1/1/NT1/3/smarttags1
To make your tag into an 'Office' tag, paste this URL: semc://liveware/A1/1/NT1/4/smarttags1
3) That's it. Now you can open the Liveware manager application to edit what your SmartTags will do when you tap them.