To partially answer my own question, there is source at the WordPress Plugin SVN of course (https://plugins.svn.ww.wp.xz.cn/photo-gallery/) but no obvious way to suggest a patch to the dev team that I know of.
Thank you, Yasin Abedi.
I will submit the idea as you suggest.
In the interim, as I plan to go forward with the modified version, if I actually put in the effort to make a new option for this (as opposed to just commenting out the code I don’t want!), I’d be happy to publish the modifications for your dev team to use as sort of “pull request.” I certainly don’t want to create a fork but OTOH I also want to move forward with the site I’m working on without being dependent on your dev team’s decisions and/or schedules.
Does 10Web have a public source repository for this plugin that I can refer to? (Besides the one at ww.wp.xz.cn’s release subversion?) (Apologies if this is written somewhere, but I’ve looked and haven’t found anything.)