A PAK version of Tidy Skillbars mod available here, which works for player using GOG version of the game : https://www.nexusmods.com/divinityoriginalsin2/mods/5/?

Install instructions: copy the .pak file and paste it in the ...\Divinity - OS2\data\mods folder.
Then activate the mod in the "mod" sub menu after launching the game.

I just did the PAK file, checked that it does not make the "usual" popup when you start & appear in the mod list. Thanks to the original mod creator and the mod testers who confirmed it worked!

For those who want to do the same for others mods, I used EE PAK extractor found here : http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=606857&page=8 to create the PAK file with the original mod. To make it completely work, I had to add a meta.lsx file taken on another mod.
SImply retro-engineer my pak file using EE PAK extractor and you will understand :)

ALL KUDOS TO THE ORIGINAL UPLOADER!