Yes it is definitely possible. When you reply to a message on your blackberry, you have the choice of picking which registered e-mail address you want the e-mail sent from.
If you have more than one e-mail configured on your blackberry profile, simply at the top of each e-mail reply, it says send using: just highlight that box and choose an alternate account.
If your account is not listed there, or is not registered with your blackberry profile, you may want to add the firstname.lastname@example.org e-mail account to your blackberry profile, simply go to e-mail settings icon on your blackberry and just fill in the necessary information.
Hope this helps.
Be sure to click Likes for those who have helped you! Click Accept as a Solution for posts that have solved your issue(s).