If you are uploading a single kit that needs all the memory of the unit, then there is no way to upload multiple kits into the unit.
I'm afraid that even when the new dump contains only a small new soundset it will overwrite *all* available memory - at least in a way that you couldn't use a potential "rest" from the former content.
When you say editor, do you mean a sound editor to allow the end user to upload their own custom sounds? If so, Alesis already stated that isn't going to happen. If by editor you mean a software interface for the DM10 to control the DM10 via your PC. Alesis has also stated that they are not going to supply that. They say they are leaving that up to 3 party developers.
Yes, i've seen that post with the excel file for the NRPN codes from Alesis. I've sent a suggestion mail to Soundquest if they could implement the DM10 in their available hardware list, because they already have implemented the DM5
An editor to upload single sounds or kits isn't essentially able to allow the user to upload their own sounds or patches. This could be prohibited by using serial codes or something similar, like Pearl does it for the RedBox soundsets.
My picture is to have another method aside the SysEx dump and to be able to add or remove only certain sets on my own if i want to.