Unfortunately, you cannot flash any game you want on any CPS PCB.

A CPS-1 is made of three boards. The CPS-B chip on your B board changes between games. On later boards, the CPS-B chip remains the same but it has a battery to store parameters, making it different.

If a game attempts to use the CPS-B registers in unintended way, the screen goes to black and is locked like this.

The Z-80 battery you mention on CPS-1.5 is to store a private key that is used to de-crypt the Z-80 instructions.

And I won't even talk about the CPS-2 because they even encrypted the 68000 code and shuffled the GFXROM there.