I mistakenly saved a script as “run only” before I was done editing it. Is there a “backdoor” way of opening it to see the code. (Of course I had (not saved another copy!!!)
There really isn’t. Your only choice is to get an old copy. Do you have any old version copied anywhere? Do you have a disk utility that can recover deleted files. If you run that before you use the computer too much longer you might get a recent version recovered.
I am assuming you aren’t in Leopard using Time Machine…
We see one of these messages half a dozen times a year, but the whole point of “run only” is to defend the code ideas and the code embedded in the script from other users – they are NOT reopenable as code. It’s a shame that that particular choice in the save menu doesn’t have a dialog “Are you sure you want this to be run only? You will NOT be able to access it again!” buttons {“It’s perfect, go for it”, “No, I might want to change it”}
For this reason Script Debugger is a bit more user-friendly.
You have to export (a copy of) the script to make it run-only 
Which is one of the many reasons I use it. Currently running 4.0.8b5.
4.0.7u here…so what’s new in the beta you’re using?
Yeah ScriptDebugger gets the nod from me as well. I’m not nearly as good at this as the advanced users on this site, but often have ambitions in that range that give me headaches. ScriptDebugger has great troubleshooting tools when I get in over my head.