Basically their are several travel offers with a landing page and when a user clicks on a offer, this should be preselected in the contact page. Can’t figured out how.
As I said, no, unless you manually edit the config file.
Better store your value in site.txt then (and add it to the site.yml blueprint to make it editable), that way it is available anywhere as well.
is there a way to change the value of the var from the front end?
If a user clicks on a button > change the value