If ur gonna use my attribute system (just search for it), you can make it run an RGSS3 method during leveling of attributes, using that you could achieve want you want to do... Though if you do use it, you'd need to make everything else too (like if an attribute would increase a param), since my script is more of a base for you to build upon.
Alternatively, you could just run a common event that checks for the value of the parameters (using KGS or Dekita's) then learn the skill when possible.
It might also be possible to do this via Tsukihime's Learn Conditions