Following the update to 4.2 mod is how I got rid of my cioscorp.
As for the IOS250 it was made with a maxed out rev. # just so it can't be overwritten by an official update, and is NOT part of cioscorp.
I did need a patched IOS70 by free the wad and the JODI mod of preloader when I was done as I updated bootmii and HBC