Adding custom graphics/content to default 'ask 'page

I know the default 'questions' and 'ask' pages are not real pages that I can edit easily through my WP site.

Is there an easy way to add custom graphics to those pages? I'm wanting to add a 'Register to add to the conversation' type of message on the page, to give clear direction to the visitors.

One other thing. The sidebar displaying on those pages seems to be some default sidebar, not the one that I've actually created that displays on the rest of the site pages. Can I make my custom sidebar display on these Q&A pages?

Thanks for your help.