As it was discovered today and verified with the 2020 Elections Committee members and Mark Waite, CIVS allows adding new voters in the current usage mode. It allows to extend the voter registration beyond Nov 08. Taking the low voting period duration and the relatively low registrations number at the moment, I see no reason to not extend the registration period. I would like to propose extending the sign-up period until November 24th (or any other similar date).
I have created https://github.com/jenkins-infra/jenkins.io/pull/3947
with a patch. The downside is that the election committee members will need to keep monitoring sign-ups and regularly add new voters, but I am willing to do so.