ok in magic.cpp find:
char checkspellskill(I32 CasterIndex, I32 SpellType, I32 SpellCircle)
{
char success = 0;

switch (SpellType) {
and change it to
char checkspellskill(I32 CasterIndex, I32 SpellType, I32 SpellCircle)
{
char success = 0;
int tempar = (calcdef(CasterIndex,0)*10);
switch (SpellType) {


Also, you have to change any CASE from (example)

case 1:
success=checkskill(CasterIndex, MAGERY, 11, 401);
break;
into
case 1:
success=checkskill(CasterIndex, MAGERY, 11, tempar+401);
break;

That's it (also tested)