How do I detect the Computer's operating system? I'm working on an emoji keyboard and it requires different input depending on the OS it's connected to. I've written the relevant methods using Arudion's default Keyboard library and can manually set which one is used. I'm wondering if there is a method or library for Arduino (currently using a Adafruit Feather 32u4 Bluefruit LE) that allows me to detect the OS. 

If not, I'll set up a switch, but that'll cost me pins.
If you can't get the OS from the USB port, why not use the existing keys/inputs to set the mode on startup? That is, if you tell the user to press different combinations of 2 buttons on startup, you have 4 (2 bits => 4 values) different paths on startup:

00 =&gt; Normal startup, don't change mode
01 =&gt; OS 1
10 =&gt; OS 2
11 =&gt; OS 3