The below code shows how to configure the help.ports option in R such that the built-in R help server always uses the same URL port. Just add it to the .Rprofile file in your home directory (iff missing, create it). For more details, see help("Startup").
# Force the URL of the help to http://127.0.0.1:21510 options(help.ports = 21510) A slighter fancier version is to use a environment variable to set the port(s):