This is the beauty of themes... just change your template!
Find your SP theme template folder - the template in question is spTopicView and the template tag you are looking for is called sp_PostNewButton(). Note in the default theme this is called twice. You will see what to change.
Remember that while in Alpha/Beta theme files will change so you may have to re-make any changes - or - the best way but again worth waiting for release - copy the theme so you can make changes we will not overwrite.