This went well, just a matter of uploading the new firmware (OpenWRT version RC5). Only thing I didn't really like was that it forced a 'secure' password, combination of lower/uppercase and numbers. Most of my home stuff had passwords that didn't fit this format, so I had to come up with something new.
Turns out that after setting a secure password, it can then be changed, and the new password checking isn't quite as strict, so I was able to use my existing router password. Nice.