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There may be circumstances where a new field is to be added to all existing content types in a SharePoint Site Collection. The result is that any new list created from an existing template or custom list will also include the (global) column if configured correctly.

The process required to add the global column is simple, but there are implications that should first be considered before applying the change.

Implication:
Adding the new column will update all existing content types, lists and libraries to include the additional column. If the column is later removed, it will remain associated with lists and libraries, but will not be linked to a content type as it would have been previously. Removing the new column completely would required that each list/library be modified (List Settings) to remove the column. Be sure that the requirements and implications of implementing a global column are considered in detail before beginning to make the change. It is important to know how the column is to be used (and by who) across the site collection so ensure that it is appropriate to implement, and configured correctly once in place.

Implementation Process:
The process to add a global column to all content types, lists and libraries in SharePoint is simple. As all content types inherit from the “Item” content type (under the List Content Types heading), adding a new column to this content type will result in all content types, lists and libraries also having the new column included.

1. Load the Site Content Type Gallery for the Site Collection (root level)
2. Find and open the "Item" content type under the "List Content Types" heading
3. Select “Add from new site columns” to add a new Global Column, or Select “Add from existing site column” to make an existing column global.
4. When adding the new column, select the "Update all content types inheriting from this type?" option if required.