Overriding flask_restx field

[Matthieu-LAURENT39]

I'm currently using marshmallow's Method field, which is mapped to the Raw flask_restx field in the type map.
However, the method field only returns strings.
Is there a way to override the type map for a specific marshmallow field, by specifying which flask_restx field to use?
Something like my_field = ma.Method(deserialize="get_field", field=fr.String) would be perfect