I can't see why a vet like you could not get TDIU, and do college at the same time. You may be unemployable now, but after voc rehab and treatment you might very well be employable. The VA should accept this as a good deal since otherwise you most likely will be TDIU and P&T one day soon.
In my day if you showed the least bit of improvement the VA would find a reason to reduce you. They are stupid really. If by supporting you now they could produce a taxpayer instead of a tax consumer that would be good from all points of view. I must be not thinking like the VA.