I don't know any way to change it without resorting to a flash programmer, especially now that you have a non-working system.
I can reflash it back to the original code if you're willing to mail me your flash in an appropriate package with return postage.
I can only do webpal flash SIMMs that have the single FLASH chip (1M). I don't have a programmer for the dual FLASH chip (2M).
Personally, I found the webpal not very compelling as a web terminal. Its more fun to hack on it as a Linux system!
Email me at the address listed at my web site and we can work the logistics.