This is revisiting a feature request from 2013 and 2015, which was declined.
A historical lock is used to retain very good or extremely useful posts that are not on-topic for a site. These questions don't meet the current topicality and quality guidelines or expectations. However, allowing them to be deleted would be more detrimental than allowing them to remain in this locked state. Most operations are prevented on historically locked questions, but moderators can edit, delete, and unlock them.
One of the disabled functions is the ability for users to raise flags, which was the request in the 2013 and 2015 feature requests. The reason for declining the feature is that flags are prevented because the questions would repeatedly get flagged. I don't follow the logic behind this rationale. After being historically locked, the question loses a lot of visibility - they fall off various question views and can only be found by searching (internally or externally). The lack of visibility should drop off flags.
The problem that brought this to my attention was a historically locked post where one of the URLs went to a dead page. The request was to update to a Wayback Machine link, which I was able to do as a moderator. However, it doesn't feel like that's worthy of making someone do a meta post. Moderators are the only ones who could do something anyway, so the ability to raise a moderator flag to request putting the question back into a state where it's actively usable is helpful. I suppose one could argue that the moderator applying the lock could or should put a cached link at the time of locking it, but that doesn't address all current historically locked posts where that wasn't done or cases where the cache may go away.
Some flags should be disabled, such as spam or rude and abusive flags, which can trigger an automatic deletion. Since moderators are the only ones who can take action on a historically locked post, it seems like a better workflow would allow users to bring up concerns to moderators via the flagging system and allow moderators to review and make a meta post if they feel necessary. This would be less impactful and someone's flow and increase the likelihood that someone would report issues with the locked posts. Reasons for review could be deleting the question if the historical significance has degraded, unlocking due to further changes in site scope or expectations, or editing to fix broken URLs to maintain the usability for anyone finding the historical artifact.
Just because a question is a historical artifact doesn't mean that it should be hard to maintain the question. Museums may not "put little bells next to each painting to summon a censor if someone gets upset about something in them", but museum curators do still take steps to maintain and preserve their artifacts so that future visitors can learn from them.