Changing Permalinks

I’ve been searching a little but haven’t found exactly what I’m looking for, I’m sure it’s gere but…

My blog is a number of years old and I have used the numeric permalink structure since day one (http://www.kevinokephotography.com/wordpress/archives/640)

I’ve been wanting to change over to the month and name structure or maybe a custom structure but this kills the old numeric structure so it doesn’t work anymore. As I have lots of links coming in so this isn’t good.

Is there a way to change to the month and name structure (http://www.kevinokephotography.com/wordpress/2009/04/waiting-for-the-light/) but still have the old numeric structure work as well?

Thanks