theres nothing in the HTA that prohibits it that im aware of. You can get dealer installed roll bars etc
Ya its one thing to install those plate covers, its somethign different to bolt in a roll bar if it was illegal. people have done it for yrs with no problems. cars like the gt3rs come from the factory with it and its legal for our roads.
as long as your view isnt obstructed out the front you should be fine.