Your best bet would be to enable SSH and do things via the command line. We operate 130 of these suckers out there and they are all setup identically. So when we change something we just do it via scripts we have created that use 'expect' (look for linux 'expect') to do nvram changes. I know you can change the SSID via nvram. It would be my assumption you can do the WPA keys too but am not for sure since we don't use encryption.
A good starting point would be to enable SSH and do 'nvram show' which will list all the nvram variables you can modify.
Also google 'linux expect' for automating some scripts, they are actually pretty easy to do.