You can set them in the file: 'C:\Users\NAME\Documents\StarCraft II\Maps\MAP_NAME\Maps\MAP_NAME\enUS.SC2Data\LocalizedData\GameHotkeys.txt'.
For example if you have a button named 'Charge' that you want to assign hotkey 'C' to, you add an entry in that file that is: 'Button/Hotkey/Charge=C'.
After saving those changes (and possibly reloading the editor to include them) you're button in the data module should have its field 'UI: Hotkey^ > Text Key' set to 'Button/Hotkey/Charge', and the 'Hotkey' value set to 'C'.
Note: If this button isn't a unique (new) button, its hotkey path may already be set in this file, and you will just want to replace its hotkey with your desired one--you don't want two hotkey entries for the same button path.
You can set them in the file: 'C:\Users\NAME\Documents\StarCraft II\Maps\MAP_NAME\Maps\MAP_NAME\enUS.SC2Data\LocalizedData\GameHotkeys.txt'.
For example if you have a button named 'Charge' that you want to assign hotkey 'C' to, you add an entry in that file that is: 'Button/Hotkey/Charge=C'.
After saving those changes (and possibly reloading the editor to include them) you're button in the data module should have its field 'UI: Hotkey^ > Text Key' set to 'Button/Hotkey/Charge', and the 'Hotkey' value set to 'C'.
Note: If this button isn't a unique (new) button, its hotkey path may already be set in this file, and you will just want to replace its hotkey with your desired one--you don't want two hotkey entries for the same button path.