I think that maybe it is important to explain the whole workflow:
-Users fill the quform, and it automatically redirects to a results page that shows some charts.
-The chart plugin can get dynamic data from an API URL in JSON, but I need that API URL to be unique to show only the user results, I mean, by his/her entry_id.
-I am resolving this by now with shortcodes, using you session variables between “add_filter(‘quform_post_process_1′” and “add_shortcode(“. So the shortcode returns a customized URL with the entry_id
-All this wouldn’t be necessary if the second file could get the session variable the same way the “add_shortcode” does. And I think it would be a bit safer because I don’t like to use variables in the API URL call if they are not necessary.
I hope I have explained it well, thank you again and again.