The only difference btwn an EF-S and EF mount is physical, not electronic. Basically, there's an extra plastic flange that sticks out, preventing a EF-S lens from mounting on an EF camera.
The "modification" referred to above relates to using a cutting tool to remove that flange. Just google it, and you'll find lots of details. Mostly, it was done when EF-S first came out and people wanted to put the 18-55 kit lens on the non-EF-S mount 10D.
In short, there's no such thing as a 3rd party EF-S mount lens. Canon has never licensed that mount to anyone, and none of the 3rd party manufacturers really needed to, it's just an extra piece of plastic.
All 3rd party EF lenses that target the APS-C sensor will typically mount on a FF camera, just a question of whether the mirror will get in the way or not. It's not just aps-c lenses that might protrude too far into the camera, many legacy 35mm lenses do as well, hence the long list at the bottom of the product page indicating that those lenses need to be modified.
The Tokina 11-16 in particular will cover the sensor on a 1.3x APS-H crop on cameras like the 1D series. It will likely mount on the EF mount Speed Booster. There's already plenty of video on youtube where people have mounted the Nikon mount Tokina 11-16 on the Nikon->m43 Speed Booster.