Multiple keyboards is no problem. If using wireless, specifically Apple bluetooth, then once one has been connected, it won't ever bother trying to connect to another one unless you force it. 2 ways of doing this:
1) Turn off your old keyboard, then turn on your new one, and pair it up
2) Manually add another keyboard in system preferences - methods vary depending on OS level
Once you have done this, then so long as both are turned on, then both will be be available to use.
The only provisos are that any keyboard bindings or setup etc will apply to both, you cannot use different settings per keyboard - they will function identically - you will need to ensure that you use different keys if you wish for 2 people to play a game using a keyboard each, or you will end up both controlling the same character. I have no idea what happens when you put caps lock on, it may or may not work on both inputs, or may be specific to the keyboard you used it on - be wary of odd things like that where perhaps a keyboard not showing caps lock is using it etc.
Also, within system preferences you may not be able to identify which keyboard is which, and things like battery level indicators etc will apply to the keyboard which connected first, not to both, and you won't know which this is. To get round this, enable the Bluetooth menu bar icon and you can view settings directly per device from the menu bar