yes you can use this method for searching an account or other(search, getObject, read from plan…).
A multivalued attribute is list of object, so you need create a list/array of the same type and put into attribute with setAttribute().
little question: Are you sure to change an account attribute in the after? with this, you have a value in SP for this attribute and another value in the target system
So I think is better a CustomizationRule, there you have the link and you can work directly before the end of operation.
Is present a variable called object where you find the link
I am just trying to understand why there is a need to update the account attribute in an AfterOperationRule and not directly in the operation request body.
If the request being sent is not updating the account attribute, could you perhaps confirm the reason for this?
It’s better to use before provisioning rule if you want to update attribute for same application .
All the operation will be serviced in one call and it would be easy for you to catch for any error or exception .