I'm unsure whether you're talking about the event sheet or the properties editor so here you go :
- in the event sheet, press enter to edit a higlighted value and then tab to navigate through the options.
- in the properties panel, tab switches from the description column to the value, back and forth.
It may not be the fastest keyboard ergonomy, but at least you can do pretty much any change using your keyboard only.
Cheers,
Nathan