Of coz switching between two videos can be made even quite easy - just synchronize V and H sync, then with use ZD at the Amiga video port switch between video (anolog) with use for example 4066 switches - this is very cheap and trivial circuit with one exception - V and H synchonization - a bit easier solution is -
http://www.amazon.com/Kworld-Externa.../dp/B000MD79PE
it accept VGA analog port and some NTSC/PAL signal - then signal is converted and overlayed/switched to external LCD monitor - this solution not give very best picture from Amiga but is inexpensive and solve some problems