I wrote a wiki page on how to use custom sprites in the particle editor.
However, this process requires you to open a text editor to create your own
.vtex file. And you have to do this for all the sprites you want to use.
My suggestion is:
Add a button where we can select a
.mks file, and then the
.vtex file is created for us, in the same folder as our original
People could easily write script which converts all
.mks files in a folder, but it would be nice to have as a part of the development tools.