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.
