This station is only staffed until five PM. There will be nobody there to change your ticket after that. Your best bet would probably be to call greyhound, directly
Not enough information to offer a response. A regular purchase yes a special might have penalties.
Yes, do expect to pay for changing a ticket date of travel. While it's not usually a problem other than the extra fee, it's subject to the bus having a seat 💺 available for you on the new date
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