Trying to get the "CALC" key on my laptop to open Galculator instead of the pre-installed calculator. I can successfully create custom shortcut with a two key (SHIFT+CALC) to launch Galculator, but as soon as I set to only the CALC key, it always opens the stock calculator. Now that I have removed the stock app, it is just a dead key, cannot assign anything to it.
I thought this would be simpler but you're right, it continues to launch the default calculator program. This is an unfortunate behavior inherited from the underlying desktop environment, Gnome, which likes to have a tight control over the system.
So, to answer your question, yes it's a bit of a pain to change this but it's possible. It does involve a couple of commands in the terminal, but should be easy enough. What we're going to do is replace the binary file of the default calculator program with a symbolic link, or shortcut, to the one you want.
Open a terminal (search for it under the applications menu) and type these two commands, one at the time:
Now, the system will try to access the default calculator that is in fact a shortcut to galculator that you installed.
You don't have to do step 1 if you already uninstalled gnome-calculator but I'm including this step in case someone else sees this.