The update_user_attributes.rb script only includes a select list of extended User Attributes, since it currently doesn't poll for and handle any/all Subscription-Specific Custom Fields for the User Object (these will vary from customer to customer, or subscription to subscription).
This Gist contains a custom version of update_user_attributes.rb that adds a handler for an Info field that is at Column 14 of an input tab-delimited text file. You may use it in replacement of the default update_user_attributes.rb script. It will populate the content from Column 14 into a custom field called "Info" that must exist on the User Object (if it doesn't, the customized updater script will fail).
You may wish to file a GitHub Issue for the User Mgmt Toolkit to request an enhancement to allow for configuration of a user-specified list of Custom Fields on Users.