Yes. As per documentation elsewhere (both this forum and many, many others) the RST button does not reset either the MMC passcode or the admin password for the web console or Installation Tool software. The RST button did reset the IP address, but since I have the MMC passcode I was able to find this from MMC811 and change it.

For context, I've worked in IT and telecoms for 25 years, so the fact that I've resorted to posting on a forum indicates that I've done the basics, followed instructions that are generally easily found, and come to the conclusion that I need to ask those with very specific subject matter knowledge for help.