doc: redefine

docs/format_content/mutability.rst

@@ -10,7 +10,11 @@ To summarize, an :term:`integrator` allows the :ref:`structured data <structured
 
    redefine
 
-      A redefine is a redefinition of all or part of the parameters of a variable as it was previously defined.
+      A redefine is a redefinition of all or part of the parameters of a variable or a family as it was previously defined.
+
+.. note::
+
+   Adding a variable to a family is not considered redefining the family. This is implicitly permitted. Redefining a family requires modifying one or more of its parameters.
 
 .. seealso::
 
@@ -112,3 +116,14 @@ If we modify the `redefine.yml` :term:`structure file`:
    └──────────────────────┴────────────────┘
 
 Here we can see that the variable has the original description, but the new type.
+
+Exception
+~~~~~~~~~
+
+We cannot change a parameter for a variable or a family implicitly.
+
+This is always true, unless you want to change the default value of a child of a custom type in a family.
+
+.. seealso::
+
+   See the tutorial with a real world sample :ref:`custom type <tutorial_custom_type>`.