Hi.

As far as I know, there is nothing line 6, or any other amp manufacturer has that will automatically tune your guitar down.  However, there is something that recently came out on the market that is designed specifically for just that purpose.  It is called the Morpheus Droptune.  It is a division of XP Audio, a company started up by one of the founders of DOD.  This pedal is AWESOME!!!  It will drop your tuning in half step decrements all the way down to A.  However, the quality of sound starts do deteriate after you drop more than a few steps.  But from Eb (which is the tuning you want) down to about C, it has hardly any tone loss.  It also has an octaver built-in.  Best $200 you can spend.  Here is the link to a video below.  Hope that helps.

http://http://www.youtube.com/watch?v=DcDvSq1pFjA

Tuning up OR down is easy with a pitch shifter.  For open tunings you will need to tune manually or get a variax.  Open tunings have strings being shifted in different amounts and even different directions.

BTW, the Spider does not have a pitch shifter of any kind... neither does the Pod series.