One marvels at the rubbish that has appeared on these pages Such gems as: Don't run up one engine at a time because of
Static stress on the nose gear assembly - even the load on the nose wheel and tail structure - and how about the writer that boasts of his vast experience and his company's impeccable safety record? Jesus wept - spare us this legend in his own mind..
I am sure the manufacturers of the Pipers and Cessna and Beechcraft light twins would either be laughing their heads off at such myths of GA - or utterly dismayed at the nonsense that is peddled by GA instructors as fact when it comes to operation of their aircraft.
Any vital technical limitation on engine handling either on the ground or in the air would be promulgated in the AFM. A local directive on the subject published in a a flying school operations manual is usually someone's (the CFI) personal opinion and not necessarily based on the manufacturer's technical fact.
Single engine run up procedure as queried by Ang737 should be the norm - unless the manufacturer recommends otherwise. I have never seen such a limitation - have you?