I have three zencarts...
Retail
Dropship
Wholesale

As of Jan 1, 2008 I will be changing the invoice numbers for all three carts.

Question:

Can I add a letter as part of the invoice number???

Example:
R2008100
D2008100
W2008100

I have found where I can change the order number and attempted to do so via the above but it didnt seem to do anything and was wondering if it was because I added a letter.