Escalation Chains for bank holidays vs standard weeks

I've only worked at MSPs that are 24/7 and have ticketing systems, so I haven't run into this situation myself. Until/If LM provides the functionality I would suggest looking it either using a 3rd party service (Opsgenie? Pagerduty?) that can provide that you are looking for or use the LM API to modify the rules in a script to make switching quick/automated.

For the LM API, looks like there is a /settings/alerts/rules/ endpoint that can modify or create rules. You can use that to modify the 92 rules for you without having to manually change each one. If I had that many rules, I likely would manage it completely in a script, Infrastructure-as-code style, so you don't need to keep both places up-to-date.