Okay so disclaimer first: This type of stuff is extremely fickle and i'm by no means an expert in WitcherScript, so it is vulnerable to being buggy. I think everything should be fine, but to test it in it's entirety i would need to play entire game with it, and i simply don't have time for this. It would take months.

It would be best to start a new game with this, but if you don't, then i added console command resetcharacter() that according to my tests enables features of the mod on existing save. DLCOnly New Game counts as loaded game btw. Command could also be used as debug tool if any funny business happens. Okay, that being said, let's go to what this mod is about:
Update: NG DLC and Saves should be handled automatically now. You still need to use resetcharacter() command if you started buying BaW Mutations tho.

To put simply - it adds more Skill Slots. 8 to be precise. To be even preciser - 6 "normal" slots and 2 slots that act as Mutation-Enabled-Slots from BaW. Given the fact that base game had only 16 slots, it adds nice and even +50% more slots. I say "normal" in quotation marks, because i haven't added mutagen-item-slot for them, because jesus christ, 24 slots are overpowered enough. To allow player to have +120% dmg more would be overkill. 

6 normal slots are unlocked after base-game 12 slots, on levels 34, 38, 42, 46, 50 and 54. 
There are no new mutations, so you get a mutation slot every 2 mutations you unlock. Before last two slots required 4 mutations instead of 2. 


FAQ:

• If you have slot locked being 9999 level requirement, it means that your slots are not loaded in correct order. For example you loaded the game from save instead of new game or used DLC-Only new game. In that case, you should use resetcharacter() console command.  Edit: Automatized this on first run
• I have in plans to make alt version that adds 8 more slots and brings total amount of new slots to nice and even +100% compared to vanilla. 
• I haven't tested NG+, so you're on your own there. Added necessary xml files, but i don't play NG+, nor do i have any plans to do so. I may hammer out any incompatibilities if i'll still have energy, because jesus christ, i worked entire week on this mod. SWF files are bastards.  
• I have plans to make VladimirUI compatch as soon as Vlad Team will feel they are content with their nextgen conversion. Don't wanna do the same work twice, but i do love VladimirUI and aim to play with it, so you can be confident the compatch will eventually happen
• I don't think it is safe to uninstall it. I may add uninstalling feature in the future. So back up your save before installing it?
• Don't ask for EE compatibility, i'll just block you. If you wanna know why, search reddits for Skyrim modding community 2022 homophobic drama and who were main culprits. Don't talk about this drama in the comments either, it wouldn't be cool to overwork Nexus staff with moderating arguments about it. I just explained why i won't support it (and why do i not permit other people to do it) and please, let's leave it at that. 
  

Lastly: It edits 3 scripts, which means that you should ScriptMerge if any of your other mods edits them. Script edits are really minimalistic, so you should be able to do it even manually if you must.

And to say it again: You have to either start new game, or use resetcharacter() console command. As far as i'm aware, skill slot IDs are baked into your save. You either need for the game to generate them at new game or use this command to do so.    Edit: Automatized this on first run

Hope i didn't scared you too much dear reader. Have fun with the mod!

Special Thanks:
Lim3Zer0 for proving to me that it is in fact possible to add more skill slots with interface for them. And i guess for giving me the need to have more skill slots
VladimirUI team for motivating me to learn how to edit SWF files and a ton of advise when i started to do it. Love ya all.