[trevius]

I don't think there is a currently a rule for that. But, it wouldn't be hard to edit that in the source if you wanted to.

in client_process.cpp

void Client::DoManaRegen() {
	if (GetMana() >= max_mana)
		return;
	int32 level=GetLevel();
	int32 regen = 0;
	if (IsSitting() ||(GetHorseId() != 0)) {		//this should be changed so we dont med while camping, etc...
		if(HasSkill(MEDITATE)) {
			medding = true;
			regen = (((GetSkill(MEDITATE)/10)+(level-(level/4)))/4)+4;
			regen += spellbonuses.ManaRegen + itembonuses.ManaRegen;
			CheckIncreaseSkill(MEDITATE, -10);
		}
		else
			regen = 2+spellbonuses.ManaRegen+itembonuses.ManaRegen+(level/5);
	}
	else {
		medding = false;
		regen = 2+spellbonuses.ManaRegen+itembonuses.ManaRegen+(level/5);
	}
	regen += GetAA(aaMentalClarity);
	regen += GetAA(aaBodyAndMindRejuvenation);
	regen = (regen * RuleI(Character, ManaRegenMultiplier)) / 100;
	
	SetMana(GetMana() + regen);
	SendManaUpdatePacket();
}

You can just change the line in RED and add or subtract whatever you want. Or you could add another line above it and multiply by something like this:

regen *= 5;

That would multiple your total regen by 5 before adding in the item and spell bonuses.