Resolution:
Only projects with the “latest” tag (i.e. the most recent copy) can be updated. Previously tagged projects are not editable. Thus, in order to modify a project in a previous tag, you must clone the project from the previous tag thereby creating a branch and then update the clone as a separate branch.

Use the following steps to clone a previously tagged project in XML Canon using the Web UI:
1. Select the category browser by way of browse > category
2. Launch the tag picker (click the by tag=”latest” link) and select the tag of interest
3. Select the project you wish to clone
4. Clone the project

Once cloned, the previously tagged copy should now have the “latest” tag as well. Start Designer and open the clone to edit like any other current project.