You have to add or duplicate a tool library as user library — then tools can be added/edited:
See: Adding tools in CC440 and later
For advanced users it is an option to manually edit the underlying .csv file. Go to Help | About | Open Data Directory, then open the Carbide Create directory and find a carbidecreate/tools directory — custom tools are stored in that in .csv files and may be backed up or saved or transferred to another computer, or edited using a text editor or spreadsheet (if one saves as CSV format). See Amana tool library