I dont think you can do this in C-script:
my.skill[10+i] = i;
Have you tried it at least?
Entities have 100 skills for quite a long time now, and I bet it's just a 100 var array named skill, too.
If you need more than 100 skills you probably need to take one of the other 2 options I've posted above. I don't have a C-Script manual anymore so I can't look it up sadly.