Мы можем использовать это в mutate
library(dplyr)
AU_PROP1 <- select(AU_PROP, base, operation, property_t, place_name, Latitud,
Longitud, currency_, price_usd, Total_m2,
usd_m2, AU_Unidad, Tramo, sector, km2, Dist_AU25M,Franja) %>%
filter(usd_m2 > 1500, usd_m2 < 5000)%>%
mutate(Dist_AU25M = replace(Dist_AU25M, Dist_AU25M==50, 25))