I guess this request is similar to Mixin with parameter support.
I share the need of kind of customizing some mixins. My team is in middle of restructuring a large project to use mixins as reusable components, thus avoiding a lot of copying-pasting code.
The thing is that in a few content-types, some (not all) of these mixins’ fields are not required (occurrence min=0). Of course that duplicating the mixin to reflect both alternatives is a valid path, but I believe it’ll largely increase the number of custom made components.
We’d appreciate the possibility of overriding a mixin’s field, which otherwise would continue with the current behaviour, presenting the default config.
For instance, we could have clean content-types representing each (bear with me) a person with a nationality (for whatever reason we could have to create a content-type specifically for each person-nation), all of them with a default mixin fullName, but some would have a middleName field shown up as required whereas the default would be not to have it. Then, again, in some nationalities we could have a unlimited maximum number of last names, and so on.
On a customizable mixin, I imagine we would be able to perform something like, for example:
<mixin name="fullName" override="middleName.occurrences.minimum=1, lastName.occurrences.maximum=0">.
Pardon me for the poor examples.