Based on your order history, it looks like you're using Piezography Selenium ink in your 3880 carts that you purchased in the beginning of 2013, is this correct?
If so, switching to a different Piezography ink tone isn't difficult- just drain the carts as much as possible, and refill with new K7 ink- keeping the shade placement the same (shade 2 always goes in the C position, shade 3 in the LC position, 4 in Magenta, etc...). You will have a few drops of Selenium ink remaining in the carts, but this shouldn't be a problem if you re-prime the carts, and draw about 5ml ink out of the exit chamber to get the new ink flowing thru the cart. After reinstalling the carts with new ink installed, do one initial fill cycle to get ink from carts to the print head, or 3 power clean cycles is the equivalent.
I would NEVER recommend reusing carts with Piezography inks that were previously used with color inks, because the color staining can never be fully removed, and will effect your Piezography inks.
I hope this helps.
Best regards and happy printing~ Dana