With v1.6.1 we could modify files using glob patterns. For example:

s3cmd modify -v --add-header "Content-Type: text/css" s3://website/assets/*.css

With v2.0.0 the above outputs an error:

"ERROR: Parameter problem: Destination must be a directory and end with '/' when acting on a folder content or on multiple sources."

I don't want to have to list out every file I want to modify and I don't want to apply the same changes to all files in a directory. It's a little unclear why this is being applied to a modify command.