Which one?

template<typename IDirect3D9N>
struct MyDirect3D9
{
    static BOOL Hook(IDirect3D9N* obj);
    // ...
}

BOOL MyDirect3D9<IDirect3D9> Hook(LPDIRECT3D9EX obj)
{
    BOOL rv = FALSE;
    rv |= VTHOOKFUNC(IDirect3D9, CreateDevice);
    // Like 5 more functions for other interfaces
    rv |= HookVTable(
        obj,
        0,
        reinterpret_cast<FARPROC>(MyQueryInterface),
        reinterpret_cast<FARPROC&>(QueryInterface),
        __FUNCTION__": QueryInterface");
    return rv;
}

BOOL MyDirect3D9<IDirect3D9Ex> Hook(LPDIRECT3D9EX obj)
{
    BOOL rv = FALSE;
    rv |= VTHOOKFUNC(IDirect3D9Ex, CreateDevice);
    // Like 5 more functions for other interfaces
    rv |= VTHOOKFUNC(IDirect3D9Ex, CreateDeviceEx);
    // Like 5 more Ex functions for other interfaces
    rv |= HookVTable(
        obj,
        0,
        reinterpret_cast<FARPROC>(MyQueryInterface),
        reinterpret_cast<FARPROC&>(QueryInterface),
        __FUNCTION__": QueryInterface");
    return rv;
}

/*
 * VS
 */

template<typename IDirect3D9N>
struct MyDirect3D9
{
    static BOOL Hook(IDirect3D9N* obj);
    {
        BOOL rv = FALSE;
        rv |= VTHOOKFUNC(IDirect3D9N, CreateDevice);
        // Like 5 more functions for other interfaces
        rv |= HookEx(obj);
        rv |= HookVTable(
            obj,
            0,
            reinterpret_cast<FARPROC>(MyQueryInterface),
            reinterpret_cast<FARPROC&>(QueryInterface),
            __FUNCTION__": QueryInterface");
        return rv;
    }

    static BOOL HookEx(IDirect3D9N* obj);
    // ...
}

BOOL MyDirect3D9<IDirect3D9> HookEx(LPDIRECT3D9 obj)
{
    return TRUE;
}

BOOL MyDirect3D9<IDirect3D9Ex> HookEx(LPDIRECT3D9EX obj)
{
    BOOL rv = FALSE;
    rv |= VTHOOKFUNC(IDirect3D9Ex, CreateDeviceEx);
    // Like 5 more Ex functions for other interfaces
    return rv;
}