The 1MB Agnus chip can handle both NTSC and PAL. It's easier to switch it in software, but you can wire up a hardare switch, too, as this seller has done.
I did that on A2000 and A3000.
A2000 there is a trace jumper you can cut and wire a switch, on A3000 there is a jumper, which I fitted with a switch, both work great.
