Why not have a condition in your automation to only turn lights on to 70% if motion detedted and they are off. That way when you have set to 100, the automation will not perform the action.
This!
As many popular YouTube videos make clear - you should always design your automations, making extensive use of conditions to ensure that the automation only executes it’s actions when you absolutely want it to.
Eg - you should have an input_boolean helper for night mode too, and as well as having a condition that prevents the automation running if the lights are already on, you would probably also want to not run the automation if the house is in night mode (eg people are sleeping).
HA can’t easily tell you if a device was last modified/changed by a person manually doing so. If you could condition for that, it would make setting up much smarter automations easier.