Xcode is VERY limited with refactoring, even with plain Obj-C. It's basically renaming and it can't even rename in comments. If it says it can't do something, then it probably can't.

The only way to rename is using find & replace. Note that Xcode can handle regular expressions so it is often good enough.

Of course, the problem is that find & replace doesn't know the programming language and sometimes can add some extra replace or forget to replace something, therefore be extra careful. Clean build is neccessary after every refactoring to check everything got renamed correctly.

You can also use command line tools (e.g. sed) to achieve the same.