I wish to have fixed content vars for use in my code in order to avoid using
hardcoded content which would require a lot of editing in case it is
necessary to change a value.

PUBLIC var AS STRING in THISWORKBOOK should do the job.

The question is where can I initialize this var to my desired content and
this initialization be done at workbook startup. How can I define a procedure
that is executed as soon as the workbook is loaded, so that inside it I can
perform any initializations are necessary? Is there a default such procedure
(whose name and existence I obviously ignore...)?