Comment 1 for bug 1827287

An example, where a flag is added to the config.yaml for the setting to indicate it's a risky move to change it:

  l2-population:
    type: boolean
    yolo: true
    default: True
    description: |
      Populate the forwarding tables of virtual switches (LinuxBridge or OVS),
      to decrease broadcast traffics inside the physical networks fabric while
      using overlays networks (VXLan, GRE).

Attempting to change it should yield a message and refuse the change:
juju config neutron-api l2-population=true

Desire state, results in:
ERROR: Changing 'l2-population' to 'true' is marked as dangerous by charm 'neutron-api'. Please consult the charm documentation to understand the risk, and indicate that You Only Live Once by adding the --yolo flag if you wish to proceed.

Adding the hypothetical --yolo flag:
juju config --yolo neutron-api l2-population=true

The desired outcome is that the change is made as normal when the flag is passed.