No its not a good idea to run the car if its trying to boost past its limiter (standard ECU is set at 10psi). No i wouldn't turn the mixture screw yourself i'd get it dont as a very minimum on a CO analyser but ideally u want it checked on a rolling road. ERST are infamous for not being able to cope with high end fuelling and its just not worth the risk, especially seeing as you are getting the exhaust manifold glowing. The chip simply unlocks the boost limit, some have a higher limit, some are unlimited.