I wanted to point out that this mapping, at least with the json provided, maps both left and right shift to the left shift keycode. This means that the only way to enter DFU mode and reflash at a later date is to open the case and use the hardware reset button. Also, many might wish to add transparency to the layers instead of N/A so shortcuts with arrow keys can be used. I have attached my modifications which only focus on minor issues like this (and RGB mode instead of backlight).

tokyo60_gusgamble.zip

Hi, I've got my brand new Tokyo60 and wanted to flash some changes into the layout, and tried the key combination from the tutorial (L_Shift+R_Shift+Pause(which was the default Fn+P) ) but it didn't work.

Thanks to the answers from the community here I've found the proper combination - L_Shift+R_Shift+B