Click the PathFinder tab.
On the PathFinder tab, click the pattern which you want to drop.
On the shortcut menu, click Drop Pattern.
Tip:
This command is only available when the Apply Edits To All Members option on the Alternate Assemblies tab is set (you are working globally).
When you drop an assembly pattern, you can then make local edits (the Apply Edits To All Members option is cleared) to an alternate assembly member.