You could use Visual integrator to import an change to the Cycle Count Value.  Probably easiest way is to use an Inventory Item Lookup Listing exported to excel.  Then modify the Cycle Count for each item and use VI to import in just the cycle count change.  If you don't use Visual Integrator for other tasks I would suggest reaching out to your Reseller Consultant for assistance.  And as always with import tools, always test into a Backup Company first, and always have a backup of the data set before importing into live companies, changes like this.  

Changing that in Product Line maintenance will only set that value on new items as they are created.  To update the cycle code for existing items you have to do that in Item Maintenance.

Use the Visual Integrator module to import into CI_Item to update items in bulk (usually from a CSV / spreadsheet import source).