1st you have tp check what dll has the GetHashFromFile Function
HMODULE hDLL = GetModuleHandleA("xxxx.dll");
DWORD dwGetHashFromFile = (DWORD)GetProcAddress(hDLL, "GetHashFromFile");
DWORD dwGetHashFromFile_Ret = dwGetHashFromFile+X;

HRESULT GetHashFromFile_Hook (
    [in]  LPCSTR   szFilePath,
    [in, out] unsigned int   *piHashAlg,
    [out] BYTE     *pbHash,
    [in]  DWORD    cchHash,
    [out] DWORD    *pchHash
){
HRESULT retval = _GetHashFromFile(szFilePath, piHashAlg, pbHash, cchHash, pchHash);
//add the retval modification code here
}

void _declspec(naked) _GetHashFromFile(){
	_asm{
	//original code here
	jmp dword ptr [dwGetHashFromFile_Ret]
}
}

void writehook(){
	DWORD old;
	VirtualProtect(*(DWORD *)dwGetHashFromFile, X, PAGE_EXECUTE_READWRITE, &old);
	*(BYTE *) dwGetHashFromFile = 0xE9;
	*(DWORD *)(dwGetHashFromFile+1) =  (DWORD)GetHashFromFile_Hook- dwGetHashFromFile -5;
}