Details
Unable to change gage factor to part copy. There is a difference between Synchronous and Ordered, when attempting to change gage, or material thickness on a part copy that was derived from a sheet metal part.
Solution
If in Synchronous...and Part Copy is in Synchronous, then just apply material and you can independently control the material thickness. The reason is because Synchronous does not support Link to File in Part Copy. You still must use Thin Part to Sheet Metal command on the part copy so that sheet metal attributes are assigned to the part copy.
If in Synchronous to Ordered for the Part Copy, if you Link to File for the Part Copy and Link Material, you'll still have to use Thin Part to Sheet Metal to apply the sheet metal attributes to the part copy. To change the material thickness, you'll do that in the orginal file from which the Part Copy is derived, since linked. When the original file has material thickness changed, it will change in the Part Copy with an update.
Notes and References
Hardware/Software Configuration
Platform: INTEL
OS: window
OS Version: 1064
Product: SOLID_EDGE
Application: PART/SHEETMETAL
Version: V219.0
Function: GAGE
Ref: 001-9247524