Dear Michel,
chatgpt proposes this code, not sure if it will work as expected. You can easily port it to FWH
#include <stdio.h>
#include <windows.h>
int main() {
  HKEY hKey;
  const char *regPath = "Software\\Microsoft\\Office\\Word\\Addins\\MacJuda.dotm";
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  if (RegOpenKeyEx(HKEY_CURRENT_USER, regPath, 0, KEY_WRITE, &hKey) == ERROR_SUCCESS) {
    DWORD value = 0;
    if (RegSetValueEx(hKey, "Installed", 0, REG_DWORD, (const BYTE*)&value, sizeof(DWORD)) == ERROR_SUCCESS) {
      printf("Value 'Installed' set to False.\n");
    } else {
      printf("Error setting value.\n");
    }
    RegCloseKey(hKey);
  } else {
    printf("Error opening registry key.\n");
  }
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  return 0;
}