1MByte memory in $00c0.0000 is always active on almost all my accelerators. The ACAtune parameter you're talking about was only valid on the ACA1230, which had the capability to switch this area on/off. However, since there is simply no drawback having that chunk of memory, but lots of advantages (like software *expecting* memory there), that mem is always active on recent accelerators.
A500 "emulation" may be possible, but please note that the original A500 has "ranger mem" in that area. That means: It's not possible to display gfx from that mem, but it's as slow as chipmem. This is a property that the ACA1221 cannot emulate.