replying to e-mails with Gmail

I'm about to buy a 16gb touch but I have a question first regarding Gmail. I have about four other accounts that gmail collects mail from through POP and gmail is configured to send mail through all of them. Is it possible to change the address that Gmail replies from on the ipod touch? I have it set to reply from the address it was sent to but this never works for me on gmails website.

 

Alright, shouldn't be a big deal. Thanks for the response.