modifying a turbo

my friend works for eriksons indutries in connecticut. He rebuilds turbos and the people that have been there longer know how to hone them out and replace the stock turbines with larger, lighter ones. does anyone know what effest this would have on the output of the turbo

You must know how to match the turbocharger if there is going to be any point with this.

In general a larger turbine or turbinehouse will make the turbocharger spool later and exhaust backpressure will be reduced.

In general a larger turbine equals increased inertia.