Windows Resource Protection

Windows Resource protection Prevents Replacement of Essential System files,Folders,Registry Keys that are installed as part of Operating System This means

I cannot replace,rename,delete essential files in System32 directory,replace Windows folder,replace critical Registry keys Unless I don't Gain TrustedInstaller Privileges and TakeOwnership Privilege, How Windows Malware Gains These Privilages ?, My Guess It first Gains Debugprivilages so that it can tamper with critical processes in system and inject code etc,Is it true Please Enlighten me ? Why does SFC /Scannow command exists does it mean while replacing system files it already has TrustedInstaller Privilage ?