Garmin Voice recognition responses...making changes

 

Anyone have any clues to making changes in the voice files that the Garmin 855 voice response system uses?
For example...once the 855 has found an address...it slowly asks "Would you like to start navigaion?"...which requires a yes/no answer. I'd like to shorten that to "Navigate?" or "GO?"...Garmins's wordy files simply slow everything down. any ideas? Thanks.
FYI....these phrases do not appear in the TTS files, and may be buried in their .....GCD files...which I haven't been able to open.

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Bruce