ToohTah, have you tried merely updating your input file in a different write/read program? Since the STAAD input file is merely a script file (aka, text file), you can tool around in it from Notepad, (Microsoft) Word, etc, etc. This way you can just hit <Ctrl> H and Replace whatever line of text (or portion thereof) in a fell swoop. Come to think of it, you can do all these operations (ie, Find, Replace, etc) in the STAAD Input Editor also.
Other than that, if you know the line number where the particular coordinate is to be found (which should be the same every time, unless the size of the model changes drastically or you renumber the nodes), you can click on the "Line x Col x" area at the bottom right corner of the Input Editor and it will bring up a nice little popup window where you can enter the line number. It'll take you directly to that line, regardless of program size. Cheers!
Roberto Sanabria