Try using MmCopyVirtualMemory

Works without disabling WP.
Requires a signed driver (Microsoft WHQL-signed or test-signed in Debug mode).

`

NTSTATUS WriteKernelMemory(PVOID TargetAddress, PVOID SourceAddress, SIZE_T Size) {
    SIZE_T BytesWritten;
    return MmCopyVirtualMemory(
        PsGetCurrentProcess(), SourceAddress,
        PsGetCurrentProcess(), TargetAddress,
        Size, KernelMode, &BytesWritten
    );
}

Thank you