You have three options that I can think of.
First option: use Safe Mode. If the restrictions are bypassed in Safe Mode, you can open a command prompt and remove the policy. In Safe Mode run:
reg add "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer" /v RestrictRun /t REG_DWORD /d 0 /f
reg delete "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\RestrictRun" /f
gpupdate /force
Then reboot normally.
Second option: use the Windows Recovery Environment to edit the registry offline. Boot into the recovery environment, open Command Prompt, determine the Windows drive letter, load the SOFTWARE hive, edit the policy keys, then unload the hive. Example:
reg load HKLM\OFFLINE "D:\Windows\System32\Config\SOFTWARE"
reg add "HKLM\OFFLINE\Microsoft\Windows\CurrentVersion\Policies\Explorer" /v RestrictRun /t REG_DWORD /d 0 /f
reg delete "HKLM\OFFLINE\Microsoft\Windows\CurrentVersion\Policies\Explorer\RestrictRun" /f
reg unload HKLM\OFFLINE
Reboot afterwards.
Third option: run System Restore from the recovery environment if restore points exist. Choose a restore point from before the policy change and let the system roll back.
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hth
Marcin