After initial install of the HSMM software on a bare-bones WRT54G, is the WRT54G operating in a Part-97 way, or is it only after changing to channels -1 or 0, or amplifying power, that one is in Part-97 mode?

I am not a lawyer, but I have spent quite some time carefully reading documentation and thinking over this topic. So, here is my carefully formulated answer:

Technically speaking, you are still operating under Part 15 rules. The only time any device or person follows Part 97 rules is when they transmit (or affix to and while under direct control...ie. RC aircraft) their FCC-Part 97-assigned call sign.

In short, anytime you identify using your FCC-assigned call sign, you are implying to the rest of the world that you and your equipment are following the rules and regulations as outlined in accordance to your license grant.

So what does this mean with respect to Broadband-Hamnet?
You and your equipment must abide by Part 97 rules and regulations as soon as you change the node name to contain your call sign. If you ever change your node name to anything else other than a call sign, then you are no longer operating under Part 97 rules and regulations, but instead fall back to and abide by Part 15 rules and regulations.

I hope this adequately and sufficiently answers your question.