OK, I think I have found what you are talking about by going back to the main site. They list a Powerchip and describe it as the original being 'surface mount', which it and nearly all the other components on the ECU are; it merely refers to the component mounting technology - mounted on the surface rather than having leads soldered through holes in the PCB. The chip is the 29F400 (just a generic flash memory chip) indicated in my picture - this is the flash memory chip where the ECU code resides. To modify the code some tuners access the contents of this chip via the 'pass thru' algorithm built into the ECU code itself; there is a protected boot loader area of the memory that holds the reflashing code that uploads/downloads the main ECU code in the main area of memory; this is the smart way of doing it since it is non-invasive. However other tuners, presumably including Powerchip, do not have access to this method for some applications and will just programme up a blank 29F400 with their code then swap out it out for the chip on the ECU. This is potentially more problematic since you need unsolder the existing chip and resolder in the replacement, or solder in a socket for it. Pretty fiddly with .5mm pitch lead components. I managed it on mine but I have access to a rework station. So to answer your question they may be able to send you a chip but you will need to open up the ECU and fit it. Actually reading the Powerchip entry for the SLK 320 I think they may just be stating the format of the chip in the ECU:
So you may not have to send in your ECU but it won't just be a simple 'plug and play' exercise either unless you are handy with a soldering iron.

Hope this helps.