(..)/mysvn/foo
(..)/MySVN/Foo

#svn up removes local copies of external resources when svn:externals is deleted
#so we need a backup
cp -R library/resource /backup
svn propdel 'svn:externals' library
svn up
cp -R /backup/resource library
svn add library/resource
svn commit -m "this will break other working copies, but we have the resource in our repo now"

svn: URL 'svn://path.to/external/resource' of existing directory
'library/resource' does not match expected URL 'svn://my.own.repository/library/resource'