Details
Added a material characteristic to a Standard Part with two values using 'Extend Existing'. A new requirement called for a third material to be added to the list of values.
Solution
Use the 'Extend Existing' command on the original Standard Parts that were extended. It gets you back to the dialog for the variable extended where you can add new values. In this case, a third material.
Hardware/Software Configuration
Platform: INTL64
OS: windows
OS Version: 10_1809
Product: SOLID_EDGE
Application: APPLICATION
Version: V219MP11
Function: STANDARD_PARTS
Ref: 002-8431897