I bypass the Personalisation option for changing in-house Personas as it doesn't seem to do what I need.
If you are confident in changing the configuration, you can change the Personas using the expert configuration. You will find this in Linux-Mint LibreOffice under TOOLS > OPTIONS > ADVANCED > OPEN EXPERT CONFIGURATION.
Search for Persona not Personas. You will find two MISC settings Persona and PersonaSettings. You can edit these string settings.
Persona should be set to own
and PersonaSetttings should be set to your individual Personas Folder and header and footer files found in the user/gallery/personas folder. For example in my Default-Personas
Default-Personas/default-header.jpg;Default-Personas/default-footer.jpg;#0000ff;#f5f5f5
Where the first # point to the text #rrggbb colour. #ff0000 is plain red in this case. The second colour setting is ignored.
You may then normally need to restart LibO for the settings to take effect. LibO 5.2 on my system seems to allow you to change the header and footer without a restart.
You may find bug https://bugs.documentfoundation.org/s... of interest.