Use R to read the geometry and attribute data with the rgdal package

r_shp.R

#(so you could modify the relationships as well and create a completely new shapefile)

library(rgdal)
## read "/path/to/files/filename.shp"
shp <- readOGR("/path/to/files/", "filename")  

## add new attribute data (just the numbers 1 to the number of objects)
shp$new.att <- 1:nrow(shp)

## write out to a new shapefile
writeOGR(shp, "/path/to/files/", "filename2")