In response to pleas from its large mortgage servicers, which have been buffeted by refinances and portfolio runoff in 2001, Freddie Mac is gearing up to launch a new "modifiable" mortgage product early next year. Although details are sketchy at this point, the new product will allow lenders to offer borrowers the ability to modify their mortgage in lieu of refinancing. The modification will be limited to a one-time reduction in the interest rate on