I found an ancient 2500 series router today and had to go through a password recovery. The rommon version was earlier than any I had seen before. The help functionality was very lean. Here is how to set the confreg for these older models.
If the rommon help screen (Type H to see it.) states that you need to type O to look at the configuration registry, you set it like this:
o/r 0x2142
I manually power cycled after this and had success. When you get things working again, I suggest backing away very slowly and cautiously.
