I don't think it includes a bundled editor app like MPD/MPK series. (I bought an APC but it was at Guitar Center and it was missing manual, USB cable, styro, and the had been used for months, they tried to pass it off new). So I ended up going launchpad +MPD for Live instead.
But on the APC's like the MPD/MPK it's super easy to edit from the units LCD section. I think the only trouble there is however many preset slots you're afforded.
Also you can just use Live's Remote mapping and save the .als file blank as a template to work around any potential preset limit.
If you really want to go crazy user definable python scripts can be used/written and people use Max4Live to take APC's to new places.
In typical Akai fashion the official statement is basically a resounding HELL NO.
"In each Live Set, you can edit what any controller or button does by going into MIDI mapping mode in Live. If you want to change how the default APC40 mapping acts in Live, you would need to purchase Max for Live, available from Ableton’s Web site. Akai Professional will not be releasing a separate template editor."
You should go over to Stray 411's nativeKONTROL site. They specialize in custom scripts for various controllers and what they do is quite impressive, and makes the prices they charge pretty reasonable considering how much their stuff can add to a controller/workflow. Especially if under the hood MIDI+scripting isn't you're cup of tea but still need the added or expanded functions.
http://www.nativekontrol.com/But overall I don't think you'll be overly hindered, but an editor is always nice if only to be able to save x amount of "snapshots" of the 20 or whatever preset slots for on the fly swapping if needed.
