Is your feature request related to a problem? Please describe.
It's not very clear that changing the "default" in the config will result in no changes for existing sessions. This leads to many questions asking why WorldEdit isn't respecting the change, when it actually is but respecting what it thinks may be user overrides.

Describe the solution you'd like

1. We add either a new flag or custom string that indicates "using global default"
2. We migrate existing sessions that share the same item as the global default to have this flag set.

Describe alternatives you've considered
Wiping the sessions folder or manually rebinding.