A T7 engine in a T5 car is doable. That's what I'm undertaking now. You'll need a throttle body from a T5, you'll have to adapt it to the T7 intake manifold with a custom spacer, you can ditch the MAF, but you'll need a T5 ECU.
Making a T7 car into a T5 car is much more complicated because the T7 computer controls entend deeper into the workings of the car beyond power and emissions. There are sensors picking up information from many more areas that would produce CELs if not corrected or, if you could even trace them all, clipped.
i don't know about converting straight from T7 to T5 but i am working on a T5 to aftermarket replacement ecu....this should allow for full tuneability however, i don't have an end product to show you....if i can go from T5 to aftermarket, you can go from T7 to aftermarket
i just put a t7 motor in my t5 car and t5 ecu and its all the same harness, theres a couple different connectors like temp guage but mines aftermarket, its pretty easy to swap to t5 pretty plug n play but i did swap TB but kept intake, went from built t5 2.3 to t7 2.0 to build on after i blew 2.3