Dynamically add SourceTag to GE modifiers

Development Programming & Scripting
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1

I have a GE for an Block attribute and I want to be able to add block chance based on different conditions. E.g. block physical attack chance, block elemental spell chance, …

I got different tags such as Damage.Physical, Damage.Elemental, Ability.Attack, Ability.Spell. Instead of creating 4 GEs for each combination I wanted to use these tags as SourceTags for a single DE_Block and add the tags programmatically in cpp.

I tried to add a function similar to this:

bool UCustom_BlueprintLibrary::AddTagsToGameplayEffectModifier(
	const UGameplayEffect* GameplayEffect,
	const FGameplayTagContainer& SourceTags,
	const FGameplayTagContainer& TargetTags
) {
	if (GameplayEffect->Modifiers.IsEmpty()) return false;
		
	auto Modifier = GameplayEffect->Modifiers[0];
	
	if (SourceTags.IsValid())
	{
		Modifier.SourceTags.RequireTags.AppendTags(SourceTags);
	}
	
	if (TargetTags.IsValid())
	{
		Modifier.TargetTags.RequireTags.AppendTags(TargetTags);
	}
	
	return true;
}

However, no matter what I try, it seems it is not possible to modify the existing modifiers. Any Idea how I can achieve this behavior without defining GEs for every combination?

Edit: another approach I tried

bool UCustom_BlueprintLibrary::AddTagToGameplayEffectModifier(
	const UGameplayEffect* GameplayEffect,
	const FGameplayAttribute& Attribute,
	const FGameplayTag& SourceTag,
	const FGameplayTag& TargetTag
) {
	if (GameplayEffect->Modifiers.IsEmpty()) return false;

	const auto Modifier = GameplayEffect->Modifiers.FindByPredicate(
	[&](const FGameplayModifierInfo& Item)
		{
			return Item.Attribute == Attribute;
		}
	);
	
	if (Modifier == nullptr) return false;
	
	if (SourceTag.IsValid())
	{
		auto Tags = Modifier->SourceTags.RequireTags;
		Tags.AddTag(SourceTag);
	}
	
	if (TargetTag.IsValid())
	{
		auto Tags = Modifier->TargetTags.RequireTags;
		Tags.AddTag(TargetTag);
	}
	
	return true;
}