Thanks, I finally understood what you meant earlier about reverting. For my purpose at least, apparently it isn't necessary to truly "unspecify" the startup trigger so long as the Refresh Timer cron job has been created. Apparently that decouples the task of starting up from the task of reloading the adblock database. And apparently that stops adblock from seeing WAN dhcp renewals as triggers.
I say apparently because in checking my recent logs, although the adblock restart "spam" is gone, my ISP has returned to longer and unvarying dhcp lease times:
$ logread | egrep 'udhcp|firewall|instance'
Thu Jan 20 04:32:00 2022 user.info adblock-4.1.3[9592]: adblock instance started ::: action: reload, priority: 0, pid: 9592
Thu Jan 20 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Thu Jan 20 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Sat Jan 22 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Sat Jan 22 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Mon Jan 24 04:32:01 2022 user.info adblock-4.1.3[29060]: adblock instance started ::: action: reload, priority: 0, pid: 29060
Mon Jan 24 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Mon Jan 24 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Wed Jan 26 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Wed Jan 26 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Thu Jan 27 04:32:00 2022 user.info adblock-4.1.3[4334]: adblock instance started ::: action: reload, priority: 0, pid: 4334
Fri Jan 28 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Fri Jan 28 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Sun Jan 30 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Sun Jan 30 18:16:03 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
Mon Jan 31 04:32:01 2022 user.info adblock-4.1.3[11095]: adblock instance started ::: action: reload, priority: 0, pid: 11095
Tue Feb 1 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: sending renew to XX.XX.XX.XX
Tue Feb 1 18:16:02 2022 daemon.notice netifd: wan (2257): udhcpc: lease of YY.YY.YY.YY obtained, lease time 345600
What's missing from the current logs is the varying lease time. In the original log you can see lease time ping pong between 3600 and 7200. I can no longer test if that difference was causing the 'ifupdate' events as posed by dave14305 in a post in the topic Firewall reloading every half an hour after udhcpc: sending renew.