You can, but the second V1210 will have to have a totally different program as it will basically be a Modbus slave to the first. You'll also have to modify the first program if you want to start and stop things with bits. This is not exactly a trivial exercise.
It would be easier to put a PC with a touch monitor on the platform and run Remote Operator.
I have a project that runs on a V1210. The control cabinet is on the first floor. The machine has a second floor platform 8' high. The operator can't see and touch the screen from the platform. I was wondering if I could use another V1210 on the second floor as a slave screen so they could see/control everything from there also. I have an extra screen that I could use. The operator has a clear view from there to the whole machine so there is no danger doing this. There are no moving parts outside of the machine anyway. Thanks in advance.
No, not at all. In fact, Unitronics will firmly tell you not to do it.
This reminds me of another thread on the forum where people are complaining because their SD card extension cable is causing issues.
If you're hacking something with non-official parts, you are on your own. Not that I'm discouraging hacking.