Then you'll need to explain further because I can do exactly this with Skill Learn.
ok well this the skill supgray the skills get stronger and the cost to use it go's up (kind of like in a mmorpg) and you can set it to change to a new skill when getting to the right level (or it can keep going till it reaches max level). i know that the skill learn system most like be used the same way but the thing i like the gimmick of work to change you skill in to a new form that has a new effet to it or it gives a buff or something like that rather than reach this level to get this skill or something like that.
say i use the skill learn system and the upgrade system and there are 2 skills i want to learn, i get them then i need to spend points in upgrading them but i need to carful pick witch i want to work on becaues one may change in to something really good that i want early on, or the ther other is better say for mostly bosses or something.
^not sure if this is the best explaintion i can give i have little hard time puting the thoughts in my head to words x-x;