Is this one of those questions where it will vary by manufacturer and type of keypad ?
A big YES on that, Holden. Keypads have differing capabilities. Some have buttons that can be reprogrammed, some do not. Even worse, it depends on what the keypads are connected to (the PLC brand and model - Allen Bradley PLC5 I think you said), whether you have access to the PLC5 program and can modify it to perform different logic.
To allow a Start or Stop with accompanying Motor Number, you would have to reprogram the Start and Stop routines inside the PLC5 program. Can you make a screen shot of the PLC5 program Start-Stop rungs for one of the motors?
Now, say belt 400 starts slipping and needs to be shut off fast. When i shut 400 off, i would want 500 and the belt further down the line to keep running.
When I program a series of conveyors, I always include interlock logic for both startup and shutdown. Then if any conveyor stops (for whatever reason) the interlock on the next one uptream causes it to stop, and the third upstream conveyor is stopped by the second one, and so on until all upstream conveyors are shut down. The downstream conveyors are allowed to keep running until manually shut down. I would bet $10 that your coal conveyor PLC logic is set up the same way, otherwise you would get some really bad spills, sooner or later.
For the start-up, the interlocks allow the fartherest downstream conveyor to start first, and the next upstream conveyor starts second, and so on until all are running.
I mean how could you set up the logic so that i could say type in "156" and hit the START button and have that motor start running.
It seems that you are using poor logic. If the Start and Stop buttons next to the keypad are presently set to perform motor start-stop for a specific motor, then most likely you will not want to (or be allowed to) change those functions.
Instead, any changes to allow a keypad (existing keypad or a new one with required additional functions) to add a new function (where the keypad becomes a control for ANY motor, not just the one controlled by the existing Start-Stop buttons) should be made totally in and on the keypad, not changing the existing Start-Stop buttons at all.
PS: Back in my young days, I spent many days at the old TVA Cumberland Fossil Plant designing and installing scrubber systems.