Modifying Values
You can modify @Config values from anywhere, as long as they are public. This includes modules that exist in Meowtils or other loaded extensions.
Warning
You should avoid doing this unless you know what it leads to, as in some cases it may lead to weird bugs or even crashes.
Modifying the value
This has to point to the module class you are trying to modify a value for, and then the field name of that value.
You will also need to manually save this to config, which can be read more about HERE.