Create default dimension with "Fixed value" on a main account

Hi everyone,

I would like to know if it is possible to create a default dimension with fixed value on a main account using x++ code. So far, I have been able to push a department value to the main account, but I can't find how to fix this department to the main account. 

MainAccountLegalEntity mainAccountLegalEntity;
DimensionAttribute dimensionAttribute;
DimensionAttributeValue dimensionAttributeValue;
DimensionAttributeValueSetItem dimensionAttributeValueSetItem;
DimensionAttributeValueSetStorage dimensionSetStorage;
MainAccountNum mainAccountId = "13000-181";
DimensionValue department = "001";

select dimensionAttribute
    where dimensionAttribute.BackingEntityType == tableNum(DimAttributeOMDepartment)
join dimensionAttributeValue
    where dimensionAttributeValue.DimensionAttribute == dimensionAttribute.RecId
join dimensionAttributeValueSetItem
    where dimensionAttributeValueSetItem.DimensionAttributeValue == dimensionAttributeValue.RecId
        && dimensionAttributeValueSetItem.DisplayValue == department;

if (dimensionAttributeValue.RecId)
{
    ttsBegin;
    mainAccountLegalEntity = MainAccountLegalEntity::findByMainAccountLegalEntity(MainAccount::findByMainAccountId(mainAccountId).RecId,                         CompanyInfo::find().RecId, true);

             if (mainAccountLegalEntity.RecId)
             {
                      dimensionSetStorage = DimensionAttributeValueSetStorage::find(mainAccountLegalEntity.DefaultDimension);
                      dimensionSetStorage.addItemValues(dimensionAttribute.RecId, dimensionAttributeValue.RecId, dimensionAttributeValue.HashKey);
                      mainAccountLegalEntity.DefaultDimension = dimensionSetStorage.save();
                      mainAccountLegalEntity.update();
             }

    ttsCommit;
}