SugarCRM CE | SuiteCRM-Add any field to Mass Update

If its a custom field that you added through studio then simply go into your sugar database and then the fields_meta_data table and find the row entry for your custom field.
Change the massupdate field from 0 to 1.

If its not a custom field added through studio then create a custom php file in this location:

/custom/Extention/modules//Ext/Vardefs/any_name.php

and then add the following code for your specific field.

$dictionary['']['fields']['']['massupdate'] = 1;
Finally run a repair/rebuild and your field should be available on mass update panel.