The Bulk Loader handles attributes in the CSV file as if they are Single Valued. It will set a value to them. See the workaround to learn how to bypass this limitation to be able to add or remove values to a multi-valued attribute via the CSV and use Bulk Loader.
Any Identity Manager version.
Consider this example:
Your multi-valued attribute is Phone Number where a user can have many phone numbers. What you can do is: you can add two new attributes to your schema, called: 'addedPhoneNumbers' and 'removedPhoneNumbers'.
In your CSV you will be able to set values to these two attributes and then build up an Identity Policy that in it's 'Add' action rule it will add the values from the 'addedPhoneNumbers' to your multi-valued PhoneNumbers attribute and in its 'Remove' action rule is will remove the values that are set in 'removedPhoneNumbers' from the multi-valued PhoneNumbers attribute.
So, let's take an example. Let's say: user already has PhoneNumbers having: "111-1111" and "222-2222". Let's say that you would like to add "333-3333" and remove "222-2222" . The result in PhoneNumbers should be: "111-1111" and "333-3333".
So, you set your CSV 'addedPhoneNumbers' attribute to: '333-3333'. You set your CSV 'removedPhoneNumbers' attribute to '222-2222'.
Now, your Identity Policy will have an Add action rule that will add '333-3333' to Phone Numbers. It will also have a 'Remove' action rule that will remove '222-2222' from Phone Numbers and so the result will be that Phone Numbers will have '111-1111' and '333-3333' as you need it to be.