Create shortcut to insert tilde or backticks

If it's just RStudio you're concerned with, you can install the Remedy add-in, and then assign a shortcut to its "Insert backticks" function.
Or check out this already existing, customisable package: Add keybinding for %<>% magrittr pipe operator

Or write your own add-in, it can be quite simple like this (not tested):

#' Insert Backtick
#' @importFrom rstudioapi insertText
#' @return None
insertBacktick <- function() {

(you then also need a inst/rstudio/addins.dcf file - you have to make a simple package I think). Then assign a shortcut to that add-in function.