Need to change the date of travel on my tickets by one day

I have sncf TGH tickets for Paris to Brussels on 7/25/14. I need it change them to 7/24/14.
I'm in US now but will be in Geneva on 7/3/14. Can I get these 2 passes changed to 7/24/14 at the Geneva station? It says no exchange, no flex, no refund on ticket?
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