How to override a third-party installation directory with inno setup

Question

I need to install a thirdparty software embedded in a installer named thirdparty-installer.exe and also install my application Instruct.exe. My application will be at c:\MyAPP folder and all my thirdparty files must be at c:\windows\system32 (all files will be thrown there, in the system32 root). I have done the following:

#define OutputDirectory_MPP "c:\myAPP"

[setup]
DefaultDirName=c:\MyAPP
DisableDirPage=yes

[dirs]
Name: {#OutputDirectory_MPP}; Attribs: system

[files]
Source: "g:\application\Instruct.exe"; DestDir: {#OutputDirectory_MPP}
Source: "g:\applicationr\thirdparty-installer.exe"; DestDir: "{cf}"; Flags: ignoreversion recursesubdirs createallsubdirs promptifolder; Permissions: system-full;

[Run]
Filename: "{cf}\thirdparty-installer.exe"; Flags: shellexec waituntilterminated 
Filename: "{app}\{#MyAppExeName}"; Description: "{cm:LaunchProgram,{#StringChange(MyAppName, '&', '&&')}}"; Flags: nowait postinstall skipifsilent

(...)

My Instruct.exe installs normally, and when it finishes, the thirdparty-installer prompts and show the user the option to change installation directory. Their default is c:\program files\Thirdparty2020\

How can I impose their installation to be on the c:\windows\system32 folder and leave no option to the user? (possibly even coupled with a silent install).