In your OnEquip script add
int nVFX=(put whatever line number corresponds to the new vfx in your modified 2da here);
if (GetTag(oItem)=="YOUR_HELMET_TAG")
{
AssignCommand(oItem,ApplyEffectToObject(DURATION_TYPE_PERMANENT,EffectVisualEffect(nVFX),oPC)));
}
And in the Unequip script add
if (GetTag(oItem)=="YOUR_HELMET_TAG")
{
effect eEff=GetFirstEffect(oPC);
while (GetIsEffectValid(eEff))
{
if (GetEffectCreator(eEff)==oItem)
{
RemoveEffect(oPC,eEff);
return;
}
eEff=GetNextEffect(oPC);
}
}