EFI_VARIABLE_APPEND_WRITE - NtDoc

#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

// Append an existing environment variable with the value of Buffer. If the firmware does not support the operation, the function returns ERROR_INVALID_FUNCTION.
#define EFI_VARIABLE_APPEND_WRITE 0x00000040

#endif
#endif
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