SetWindowsHookEx->Modding keyboard input

[Quell]

Hey.

if (nCode == HC_ACTION)
	{
		KBDLLHOOKSTRUCT* kbh=(KBDLLHOOKSTRUCT*)lParam;
		switch(kbh->vkCode)
		{
			case 0x41:
				{
					INPUT bKey;
					bKey.type=INPUT_KEYBOARD;
					KEYBDINPUT kbinp;
					kbinp.dwExtraInfo=0;
					kbinp.dwFlags=0;
					kbinp.time=0;
					kbinp.wScan=0;
					kbinp.wVk=0x42;
					bKey.ki=kbinp;
					SendInput(1,&bKey,sizeof(INPUT));
					return 0;
				}
		};
	}
    return CallNextHookEx(NULL, nCode, wParam, lParam);

Now the Hook proc gets called alrite and all, however i want to modify the input once it was hooked.
The above code definetly does not work, so i was wondering how can i modify the input that i hook? basically what happens if i press 'a' is i get 'bab' as output.
Thx