Ability to remove - 'Use Existing' on certain Single/multiple relationship fields

When using these links (which are very powerful) It would be great if we could turn off the ability to use existing fields for specific usecases - mainly to avoid clients from choosing one, then making an edit to the link therefore affecting all other linked fields to that model.

Basically just as a saftey feature - it would be great if this was in the linked field setup area (validation maybe)

The opposite (removing the ‘create new’) would also be really useful in certain scenarios