You can't change the internal functioning like that.
What you can do is:
- Map the mouse keys as alternative keys, assuming the game will detect the input (it probably won't).
- Map the mouse keys to the keyboard keys, with a macro on Razer's software or Autohotkey (not recommended).
You just have to remember where the skills go.
However, I think you can add a 2nd layer of skills, where you can use the extra space as visual help.
I would leave 1-3 as the least used skills, and 10-12 as the most used skills.
I think it is possible to make your own Reshade overlay and show it over the game, where you show where each key is and what it does.