Biztalk Rule Engine

Hi,
I want to update the value of an element in the action of a rule, by concatenating a new string in the old value. I have not found any function available for this. I want to do this so that i can find out which rules have failed in the output.
for example I want to do something like this.

Schemas.BillsSchema:/CreditBills/CreditLines/ErrorReason = Schemas.BillsSchema:/CreditBills/CreditLines/ErrorReason + \”,Rule 2 failed\”.

Also I want to go for checking the Others Rules in case one of the rules already failed.

Thanks in advance.
Regards.