@mariosv Did not work for me - clicking around in “Additional formats…” I occasionally am getting an active “insert” button, but I am not able to effectively set and reference a variable this way. I suspect there is a bug that needs to be fixed.
I am able to create the desired field by renaming a test file to .zip, editing content.xml, and adding stuff like office:value-type="string" office:string-value="my stuff here"
for the setting field. then renaming the file back to .odt
I am hoping there is a way to do this without resorting to such direct tinkering in the file