Nothing unusual about swapping the 3 & 4 blade props around. The first time I got involved was when the gear was selected up on a BBMF Hurricane at Northolt, my first day with BBMF! Shortage of 3 blade type meant fitting a 4 blade.
Usually the basic blade angle is adjusted as often the reduction gear ratio is different and this would affect the reference/static rpm.
Some propeller manuals also give the required basic blade angle change required when the propeller is cropped or different diameter prop fitted.