Odd Mod to an HD-130 (Extra Switch)

I was recently excited to see a well priced HD-130 pop up on Facebook Marketplace in my area. After talking to the seller, he sent a couple better photos of the amp and I noticed it has an extra silver switch in between the standard Deep and Power level switches.

Despite, or perhaps because of, the seller insisting it was unmodified I reached out to Ed Goforth to ask if he had any ideas. He was able to confirm my thought that this certainly isn't a stock switch, but wasn't sure what it might be meant for beyond that.

The seller explained it as a power switch and that it took precedence over the 3-position switch which was now a stand by switch. This makes little sense as the stand by switch is still on the back, though appears to have also been modified at some point. In talking with the seller I learned that it had been living and gigging with a Djenty Death Metal band in Portland before he bought it and brought it out to New York.

I was curious if anyone on here had any ideas about the purpose of this or even recognized the amp or mods? I won't be following up with this as I am very cautious about buying used Tube Amps, certainly those that have clearly had some level of non-standard repair or unknown modification.

Thanks!