In what way? And i guess it just goes under 100% damage without any extra effects to it. But if you want, I think taking this part of the code:
int battle_calc_skillratio(int attack_type, struct block_list *src, struct block_list *target, uint16 skill_id, uint16 skill_lv, int skillratio, int flag){...}
and adding this inside:
case BF_WEAPON: switch( skill_id ) { case ITM_TOMAHAWK: skillratio (+-=) x; (Add a needed skillratio here, for example half the attack would make it skillratio -= 50) break; case SM_BASH: case MS_BASH: skillratio += 30 * skill_lv; break;
Untested, but might work.