It should be impossible to negotiate this with individual policemen - if the state or municipality has the requirement and authority to provide security for something, then the conditions for that should be handled by the government (and then the officials would execute that as part of their ordinary non-negotiable orders of what duties their service requires), and if the government does not do that thing, then police officers should not be involved at all, this should be handled by private security, in which case even if someone from police participates off-duty, they shouldn't be permitted to have uniforms/badges/official authority, as they are not there as representatives of the state but as civilians.

There shouldn't be any middle ground - either the government sends the police to do whatever the government requires, or it does not - the policemen themselves should not get a choice, they exist to execute and enforce the government decisions, not make them.