The following workaround lets you change the Preferred Memory setting on locked applications either shared by an AppleShare File Server, or on your local hard disk:
1) Open Get Info dialog box for the application file.
2) Unlock the file if it is locked.
3) Close the Get Info dialog box.
4) Open Get Info for the application file a second time.
5) Change the Preferred Memory setting.
6) Close the Get Info dialog box.
7) Open Get Info for the application file a third time.
8) Lock the file.
9) Close the Get Info dialog box.