Is it possible to create my own custom attributes?
Yes, it is. The CustomAttributes example provided with Visual C++ .NET demonstrates how to do this.
Can attributes be used in native (straight) C++?
Yes, it is possible, but there aren't many attributes available for this. The source code for this book contains a native C++ project using attributes for event handling.
Can you cut and paste the source code from a merged source file and use that code in place of attributes?
Yes, you can, but it is not recommended. Keep in mind that if you need to change the code later, it will be much more difficult using source code than it would be to just change an attribute.