It is possible to manually change the SharePoint Timer Service account:
- From a command prompt change to the directory where the SharePoint Timer Service is running C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN
- Run the command stsadm -o updatefarmcredentials -identitytype configurableid -userlogin domain\account -password password
- Once you have run this command restart IIS
That's a quick post with not much else I can share for now. Enjoy!