hmmmm it's complicated to me xDThats not really possible. The World Editor is very limited when it comes to abilities. You can copy them, you can change their values, but you can not really create anything new.
What you can do though is cheat a little. Here is how it goes:
1) You create your seperate cleave and critical strike abilities.
2) You create a copy of the Spellbook ability.
3) You add both of your custom cleave and critical strike to the spellbook.
4) You set the spellbook to "hidden". This way it will not show up on the unit who has it.
5) If you add this spellbook to a unit (via triggers for example) the spellbook will not be shown, but the passive abilities inside will still work.
6) You create a passive ability without an effect (there are many such abilities in the game). This purpose ability is to show the player an icon with a tooltip and description. You add this ability to the unit as well.
That is one way to do it. It is a little bit complicated, sure, but it works reliably.
I found a guide xD https://www.hiveworkshop.com/threads/leveling-spells-in-spellbooks.168418/I cant remember anymore whether you could level up the abilities within a spellbook via triggers. If not you can still replace the spellbook with a different spellbook which contains the higher level versions of the passive abilities.
Things being complicated is the norm in the WE. Whenever you want to do something that wasnt in the original game things will get messy and complicated.