If you don't want your software to change, don't update it.
The way Thunderbird looks and the messages list is a large part of it is horrendous and is a deal breaker for me, for example.
Cloudflare's status page is one of the very few services of Cloudflare that are hosted elsewhere precisely for the reason it needs to be available if something isn't working.
It's very difficult if not impossible to create a staging environment that would well enough replicate production at this scale. What bog posts suggest as a remediation in the process:
"There are several opportunities in our automation suite that would mitigate some or all of the impact seen from this event. Primarily, we will be concentrating on automation improvements that enforce an improved stagger policy for rollouts of network configuration and provide an automated “commit-confirm” rollback. The former enhancement would have significantly lessened the overall impact, and the latter would have greatly reduced the Time-to-Resolve during the incident."
Customers can create firewall rules to challenge requests using any type of request metadata. User agent is one of the filters, that can be used in manual Firewall fields.