If you have FileMaker Advanced, you can launch FileMaker, enable the script debugger and then open the file. The start up script will come up in the debugger and you can halt the script and then correct it.
Without FileMaker Advanced you may still be able to get the file open without performing this script. If you have some other script in the file that is safe to perform, you can open or create a new database file and run a script in it that uses perform script to perform the "safe" script in the other file. Then you select the file from your Windows menu.
And protecting against "developer remorse" is one of the reasons behind the ideas in this thread: Saving Sequential Back Ups During Development