Since the vendor_lead_code field is present in the vicidial_hopper table(which is a memory table) we are not going to change this in our default settings. MEMORY tables cannot use VARCHAR fields, and must allocate all of the memory even if the field is empty. You could certainly make this modification on your system, but we aren't going to lengthen this field by default at this time.
Here's how you would do this on your system in MySQL:
ALTER TABLE vicidial_list MODIFY vendor_lead_code VARCHAR(36);
ALTER TABLE vicidial_hopper MODIFY vendor_lead_code VARCHAR(36) default '';
Referenced,
http://www.vicidial.org/VICIDIALmantis/view.php?id=766