Yeah these are good suggestions. The "address already in use" error suggests that you might have multiple copies of arc running, so that you're making changes to the wrong copy. Use the commands 'ps' and 'kill' to look for the other copies and stop them.
I used the command
ps aux | grep 'news.arc'
and it returned only one copy running, but I suspect that's not right.
And your comment about multiple copies also got me thinking that from the main Arc directory to go into the Arc prompt maybe I shouldn't have been using
$ mzscheme -f as.scm
Was I supposed to use that just once to run news.arc for the first time?
Assuming you're using 'GNU screen' you also have the option to re-attach to an existing session using the 'screen -r' command. Using 'screen -ls' will list out all the sessions should you not be sure, or have more than one.
That aside, most developers will do development changes on a local machine where they need not attach/reattach and this way you wouldn't need to troubleshoot your code and the host environment at the same time.
Then you create a stable deployment process. eg. Backup the old code, drop in the new code, re-attach to the existing session and either load your changes or restart the program if you're ok with some nominal downtime.