FYI this setting doesn't do what you guys think it does...
Applications need to have <longPathAware>true</longPathAware> in their app.manifest before it's able to take advantage of this setting and at present there are no apps that have done this - other than Windows Store apps.
E.g. Explorer and every other last application will still have a 260 character limit even after you enable the setting.
You will need to force older applications to use this setting by enabling an option to force windows to load external manifests from the application folder overriding the manifest that's compiled into the executable:
1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type PreferExternalManifest, and then press ENTER.
5. Right-click PreferExternalManifest, and then click Modify.
6. In the Edit DWORD Value dialog box, click Decimal under Base.
7. In the Value data box, type 1, and then click OK.
8. On the File menu, click Exit to close Registry Editor.
9. Reboot.
Then in the application folder:
1. In the same folder as the executable, create a file with the same name: photoshop.exe.manifest or notepad.exe.manifest etc...
2. Paste the following XML:
Long Path Aware sample manifest · GitHub
3. Save and exit the file.
4. Try running the application.
The problem with overriding the manifest that's been compiled into the executable is that you might omit critical dependencies or other configuration that the application requires from its internal manifest... You might need to use a PE editor to find the manifest inside the executable, copy the XML into the external.exe.manifest that you created then add <longPathAware>true</longPathAware> instead before it'll work properly...