Nspire student software has to have the ability to read the os of the ti-nspire. There are four ways that we might just be able to get past this ability (tell me if I am wrong):
1. Trick nspire student software into "fake-reading" the os of your nspire, allowing you to downgrade it.
2. Create a program that scans for downgrade protection in a ti-nspire os image, and removes it.
3. Create a new linking program that allows you to downgrade your nspire.
4. Downgrade ti-nspire student software.
Numbers 3 and 4 are most likely to be possible, whereas 1 and 2 may seem slightly.. er... dumb.