Hi dmichael, you need a space after open.
To make it a little better, in your applications folder run AUTOMATOR, create a new APPLICATION, search for RUN SHELL SCRIPT, drag it into your workflow, remove the default CAT line, type in (minus quotation marks):
“open /Applications/Unreal\ Engine.app --args -noselfupdate”
then save your file.
Now all you have to do is double click the file you just created.