Is there a way to view/edit Outlook for Mac's SQLite database to edit the signature file?

Solution 1:

Microsoft Outlook for Mac v16 stores signatures in a proprietary .olk15Signature (aka .olk15) file format under the directory /Users/youruserid/Library/Group Containers/<guid-like-string>.Office/Outlook/Outlook 15 Profiles/Main Profile/Data/Signatures/<NNN>/<guid>.olk15Signature. While .olk15 files do contain a section with UTF-16 encoded HTML, the header and footer formats are opaque. The Outlook.sqlite database's Signatures table stores references to the .olk15 files in its PathToDataFile column.

Solution 2:

You can access it using the built-in SQLite program. In Terminal run the command “sqlite3” with the your Outlook.sqlite file as the parameter.

From there you can use SELECT commands to view data and UPDATE to change them. Check the SQLite home page for documentation, if you do not already know SQL.