Enter new column names as string in dplyr's rename function

I think this is what you were looking for. It is the use of rename_ as @Henrik suggested, but the argument has an, lets say, interesting, name:

> myFunc <- function(df, col){
+   new <- paste0(col, '_1')
+   out <- dplyr::rename_(df, .dots=setNames(list(col), new))
+   return(out)
+ }
> myFunc(data.frame(x=c(1,2,3)), "x")
  x_1
1   1
2   2
3   3
>

Note the use of setNames to use the value of new as name in the list.