NtSetSystemEnvironmentValueEx - NtDoc

#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

NTSYSCALLAPI
NTSTATUS
NTAPI
NtSetSystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _In_reads_bytes_opt_(ValueLength) PVOID Value,
    _In_ ULONG ValueLength, // 0 = delete variable
    _In_ ULONG Attributes // EFI_VARIABLE_*
    );

#endif
#endif
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#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwSetSystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _In_reads_bytes_opt_(ValueLength) PVOID Value,
    _In_ ULONG ValueLength, // 0 = delete variable
    _In_ ULONG Attributes // EFI_VARIABLE_*
    );

#endif
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