EXTRA_F1, EXTRA_F2, ... EXTRA_F10: left hand side function keys, named from left to right, then from top to bottom

F13, F14 ... F24: function keys upper row from left to right, like the legends say.

LANG_4: Central key on the cursor block 

ESC: upper left corner on number block
NUM_LOCK: second key on the first line of the num block
SCROLL_LOCK: third key on the first line of the num block
EXTRA_SYSRQ: upper right corner on number block
PAD_ASTERIX: second row, rightmost key on the number block
PAD_MINUS: third row, rightmost key on the number block
PAD_PLUS: fourth and fifth row, lower right corner of the num block, double sized key.

EUROPE_1 (only on ISO keyboards): key directly to the left of the ISO big Return key in the ASDF row. Should be mapped to BACKSLASH to work as expected. 

open a dos prompt. navigate to your tools folder and drag&drop scas.exe to the command prompt, but don't run it yet. add a space to the end and then drag&drop your custom .sc file to the end of the command line - don't run it yet. add a space and then drag&drop the same .sc file - and then add a B to the end. now hit enter to run the command. this "compiles" your code. you will find it in the same folder as your SC file but with SCB as the file extension.

now that your custom file is compiled, you need to send that to the teensy. drag&drop scwr.exe into the command window, add a space, and then drag&drop your .SCB file to the end of the command line. hit enter to program.

test your newly remapped keys to verify that they are remapped.