Firstly the identify numbers don't matter for anything. They are just there so when you ask Windows to "identify" they put the numbers on the screen and it shows you in the UI. They serve no other purpose. So personally I don't see why you would care about this at all.
However the actual numbering comes from the order in which you have them plugged into your graphics card. Windows ultimately just asks the gfx card for the "connected" monitors and it returns them. That becomes the "identity" of the monitor as it were. So if you were using the same cable for all the monitors then you could "renumber" them by changing the order that you have them connected. But this would also potentially impact the primary monitor setting and also which monitor gets the BIOS messages you see (depending on your motherboard).
Again, the identity numbers have no meaningful use so I would leave them alone. But I have heard that it is possible to change the cached value in the registry. But I don't know where that setting is.