[R] Overwriting a procedure

[Steven Yen]

Is there a way to over-write a procedure (subroutine)?

I include a default procedure fixx in a list of procedures which are 
compiled into a package. By default, the procedure deliver the data matrix x.

fixx <- function(x){
result <- list(x=x)
return(result)
}

In some applications, I have transformations (such as squared terms) 
in some column(s) in x. So I include the following procedure in the 
mail (calling) program, hoping to over-write the default procedure 
under the same name in the package (which is the way other languages 
works, e.g., Gauss):

fixx <- function(x){
x[,6]<-x[,5]^2/10
result <- list(x=x)
return(result)
}

This does not seem to work. The procedure in the main (calling) 
program seems to get ignored. Any idea? Thanks.