I wouldn't use a serial generated field because you can not modify the next number from script or disable the auto generate from script. I would create my own field to hold the next number and then set this field by script as needed, which then populates your control number field.
Thanks.. what I ended up doing was create the beginnings of a Preferences Table. Created my starting Control Number field there... and then through the script I have running it goes through and sets the fields with that control number and another calculation increases the number by +1
My control number looks like this FCR2014-0001 so I decided to use the SerialIncrement function to keep text intact. ;)
works for me. :)