This R package applies the corrections to the Polity coding according to Vreeland (2008) and Plümper & Neumayer (2010)
You can install it through
install.packages("devtools")
library(devtools)
install_github("felixhaass/recodepolity", dependencies = TRUE)
library(recodepolity)
output_df <- recodepolity(file = "http://www.systemicpeace.org/inscr/p4v2015.sav")
output_df contains all the recoded variables, for variable names see help(recodepolity)