Here is a short item from a case handled by Saikat Bhattacharya:
Question: How can I define keyboard shortcuts for external commands in the Revit 2010 add-ins tab?
Answer: Shortcut keys for Revit are defined by adding entries to the file KeyboardShortcuts.txt. This file is located in the Revit Program folder, together with Revit.exe and Revit.ini. It contains a commented header section describing how to construct a new shortcut key entry.
A shortcut definition consists of a line specifying the key sequence, an action type and the action string. The key sequence is quoted, the action type is 'ribbon' for add-ins, and the action string is the hyphen-delimited path to the ribbon item to activate. Example:
"WA" ribbon:"Home-Basic Modeling Tools-Wall"
Since add-ins are located in the ribbon, the action item for an add-in will always be 'ribbon'. To specify the Add-Ins tab, you need to replace the hyphen by an underscore, because the hyphen is reserved as a separator character in the keyboard shortcut definition. Therefore, the first item in the shortcut definition for an external command is 'Add_Ins'. The next items specify the panel name, which is 'External', followed by 'External Tools' for the external commands pulldown button. So for a simple external command named XyzCommand in Revit.ini, the complete keyboard shortcut definition might be:
"XYZ" ribbon:"Add_Ins-External-External Tools-XyzCommand"