Question: I need to install a couple of installers in the same directory so it conflicts with the Inno Setup uninstaller name `unins000.exe` and `unins000.dat`

Is there a way to change the default name of an Inno Setup uninstaller?

Answer: 
Inno does this automatically when it detects a different application being installed into the same directory (based on a different [`AppID`](http://www.jrsoftware.org/ishelp/topic_setup_appid.htm)). There should be no need to go behind its back and rename the uninstaller files.
Inno Setup does not offer any way to let you name (or rename) the uninstaller. Inno Setup takes care of naming conflicts on its own.

Also note that when you try to rename the uninstaller manually (like some answers here do), you break the reference to the uninstaller in *Add or remote application* in Control Panel. 

Even if you fix the reference, there's another problem. When you upgrade later, the new installer won't find logs of the previous installer and won't be able to merge them. Consequently a future uninstallation won't completely remove the application. See the [Appending to Existing Uninstall Logs](https://jrsoftware.org/ishelp/index.php?topic=appendnotes) in Inno Setup documentation.