If I understand the question, no you can't edit the .DLL. You have to change the code, compile it, then replace the .DLL file with the new one. With InstallShield, you can make a patch installation that will make the necessary changes to the .DLL file, but it needs the original .DLL file and the new one to build the edit patch because the edit will only work on the version of the .DLL file. It's a heck of a lot easier to just unregister and replace the old .DLL file with the new one and re-register.
Dave Kreskowiak Microsoft MVP - Visual Basic