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Merge strategies are used to control merging of overlapping options from the Options API & mixins when the component is created.
Special handling of style and class props is a runtime thing and it works only because Vue devs decided it is a useful thing to do and implemented it that way.
What you want is not possible unless Vue devs decides to implement it… which I doubt – because implementing it for class and style is straightforward as the "output" is well defined by HTML standard. Implement the same thing for any prop is much more difficult because you don’t know the data type of the prop in advance (as opposed to class and style) – i.e. how would merging work if the data type of the prop is Number or String ?
TL:DR
It is not possible. Move on…