The Manage Category Assignments feature allows you to pick a Category/Subcategory and Page Type and assign these Categories/Subcategories to specific Shapes as well as giving you visual feedback as to what Shapes are assigned to which Category/Subcategory. This is a good interface to assign or re-assign multiple Categories/Subcategories to a single Shape. This is the opposite of the Manage Shape Assignments feature.

In the D-Tools SI window within Visio, click the Manage Shapes button and select Manage Assignments > Categories.

This will open the Manage Category Assignments form.

Select the View Type in the ribbon:
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On the left side of the interface, select Categories and/or Subcategories for which you want to assign a specific shape and click the right-arrow to add to the right-side of the interface.

Click Assign > All:

This will open up the Assign Shape for Categories form. Select a shape and click the Assign button.

The assigned shapes will display:

If you want a "clean slate" to work from, you can choose to unassign all existing Category assignments. Be warned, that this action can not be undone for any user assignments. However, you can always reset to the default pre-assignments from D-Tools.

In the D-Tools SI window within Visio, click the Manage Shapes button and select Manage Assignments > Unassign Categories.

This will open the Delete Category and Shape Assignments form.

Check the Page Type for which you want to delete the assignments and click Yes. This will display the following warning.

If you ever want to restore the default pre-assignments from D-Tools, in the D-Tools SI window within Visio, click the Manage Shapes button and select Manage Assignments > Categories. On this form click the Restore Defaults button.