I posted a response in your Steam thread that might contain the solution. Did you try that?
Edit: Okay, I've added the keybinds and put in a reference in your script to call those keybinds. (Also, gotten rid of the boatloads of extraneous localization and added some you overlooked.) Testing as soon as the game comes up.
Re-edit: Intriguing. It would seem that the game does not take kindly to attempting to redefine an enum that has already been defined. My tests yesterday worked, but I modified the base file directly instead of using mods.
I'd bring this to Lucas' attention in the IRC (if he and Reaper haven't already noticed the two threads you opened on the topic, that is
, as it sounds like a bug. (Or, if not a bug, then something that needs some expert guidance from a dev to figure out.)
In the meantime, I have these observations to make:
1. You do not need to override locales/ui.txt. You can make a locales/ToolMod_ui.txt and put your locale keys (DESIGN_REPLACE_TOOL and KB_DESIGN_TOOL_REPLACE are needed, with the latter being modeled after KB_DESIGN_TOOL_# in locales/options.txt) in that file.
2. Once you define your keybinds correctly, you will need to make sure the design editor knows what to do with those keybinds. You probably already noticed that and left it out because you couldn't get the keybinds working, but I'm mentioning it just in case.