Referring to these instructions is it possible to not alter the Travelify original files and carry this out in the child theme instead?
It is not easy but it is doable. Since all changes that should be done are not part of basic Wordpress template files, all changes to these files should be done via Child Theme functions.php file.
The tricky part here would be to disable default slider scripts and enable them again via Child Theme but without
if statements. here is how you can disable script via Child Theme https://wordpress.org/support/topic/theme-portfolio-press-functions-for-child-theme?replies=11
Thank you Aigars! I will investigate.