PeopleUpdate allows you to edit multi-valued attributes in Active Directory. With multi-valued attributes, the Edit page shows multiple text boxes with an Add button to allow you to add and delete values to and from the attribute. In some cases, though, you may have a multi-valued attribute in your Active Directory schema that shows up as an editable single-valued attribute on the PeopleUpdate Edit page.

Use the procedure here to add your multi-valued attribute to the PeopleUpdate configuration. Once finished, the attribute will be editable like the Website attribute in the screen shot below.

Background 
PeopleUpdate queries the Active Directory schema for each attribute to determine whether an attribute can store single or multiple values. Depending on whether the attribute is single- or multi-valued, PeopleUpdate will show an appropriate editing interface on the Edit page.

To show a multi-valued edit interface for a multi-valued attribute:

1.Using an XML editor, open the LdapMapping.xml file in the application configuration directory, typically located at %Program Files%\WebActiveDirectory (for versions prior to v3.4 SR #1) or %Program Files%\WebActiveDirectory\PeopleUpdate (for versions including v3.4 SR #1 and later). This file contains attribute mappings for LDAP attributes in Active Directory and PeopleUpdate uses the mappings to query the AD schema and determine if each value is single- or multi-valued. You should create a backup copy of this file before making modifications in case something goes wrong and you need to restore the backup copy.

2.Look for an LDAP attribute element that you want to copy as a model for the new multi-valued attribute to add. An example looks like this:

3.Copy the entire ldapAttribute model element and add it to the end of the list (or alphabetically if you like) as a new element.

4.Change the ldapDisplayName and ldapName attributes of the new element to the proper values for the multi-valued attribute. You can get a list of all default AD schema attributes, including their internal LDAP names and LDAP display names, at https://msdn.microsoft.com/en-us/library/ms675090(v=vs.85).aspx

5.Save the changes to the configuration file.

6.Navigate to a PeopleUpdate Edit page that has the attribute and ensure the attribute is rendered with an edit display mode for a multi-valued attribute.