if we are going by the blue posts and equation blizzard explicitly stated is used to award RP every week, there is no separation of the decay term with the awarded RP every week. If you change the rate factor you necessarily scale decay and awarded RP by the same amount. The only way to change decay individually is to foil out the terms and relabel the rate factor :
blizzards equation : current RP + (expected RP in bracket - current RP) * rate factor
Equation with separated terms : current RP + expectedRPRP_rate factor - current RPdecay factor
which simplifies to currentRP* ( 1 - decay_factor) + expectedRP*RP_rate factor
So yes, technically speaking there is a world where the variable for rate factor is divided into 2 separate terms to scale decay and RP differently, but I have seen no evidence that Blizzard has done this, and in fact, to do this breaks the intended functionality of the system. The ONLY solution to a 6 week ranking progress using blizzard’s actual method of awarding RP is to change the rate factor to .4 or 40%.
As stated by blizzard,