Thunderprop replaces your build.prop.
I highly recommend against flashing it over our builds. I have made a custom thunderprop for the CM7 variants. You would have to pull out the one for your build of CM7.
As for another note. The thunderprop was built for the GB version of the thunderbolt (it's what our phone would look like in the play store) so if you flash it, you will show up as GB, not ICS.
As for the responce I saw about the phone acting weird, I don't doubt it will screw things up. There are a bunch of settings in the file. Some that are dependant on files to be there on not be there. And if you are loading ICS with one kind of video drivers, but the build.prop call for a different set of drivers.... Well you get the point.
And before I go look myself, does the thunderbolt have ICS?