In XVI32, why is 'File access denied' still after selecting 'Run as Administrator'?
That's probably because iexplore.exe is owned by TrustedInstaller (NT Service\TrustedInstaller). You may have to take ownership of the file first (and backup the file) before modifying.
After editing, change the ownership back to NT Service\TrustedInstaller
Thanks to this answer, I Googled myself how to 'Take Ownership' and found this.
But the solution was simply to Right-Click the .exe file, then access the Security tab, and then to allow Permissions for Everyone by using To change permissions, click Edit. 