Since "XSD" is the W3C XML schema language controlled by W3C,
you cannot redefine anything in it.
Specifically, you cannot redefine anything defined in http://www.w3.org/2001/XMLSchema
namespace!
And how could you? After all, whatever you do,
you always need to start from the normal <xs:schema>
element, which is already defined in that namespace, and 'defined' means here that any possible content of <xs:schema>
is already defined as well.
There cannot be some kind of bootstrapping here!
That would be a different language then. (Although a curious idea indeed -- write it down and send to W3C!)
Well, what you can do is to define your own XML schema language (e.g. 'XSDX')... but in different namespace, and, yes, you can base it on the standard XSD. Just import http://www.w3.org/2001/XMLSchema
namespace and reuse any constructions defined there (that is global components). What could be use of that 'XSDX' language is a different story... (I guess, you'd have to develop some kind of new software to work with it.)
However, I guess, your actual goal is to validate your XML schemas for compliance with some aditional requirements (e.g. about that "type" attribute).
You can achive this by developing some kind of extra-validator.
Alternatively, you can replace (temporary) the http://www.w3.org/2001/XMLSchema
string in your schema(s) with the URI representing your extended XML schema language.
Then, any standard software would think it is just yet another XML and do with
it any validations or whatever else. However, a full-blown defintion of your extended
XML schema language -- in the form of some (normal) XML schema for it -- will still be needed.