Access response_object/@body return in after filter

I am attempting to implement API versioning ala Stripe (https://stripe.com/blog/api-versioning).

I currently have a working prototype that hooks into Grape before/after hooks – but to modify the response I have to reparse and regenerate the JSON from response.body – when obviously I would prefer to hook in earlier and muck with the hash before it's jsonified – it also means I have to correct the headers e.g. Content-Length, if I want those to be correct.

I see in https://github.com/ruby-grape/grape/blob/master/lib/grape/endpoint.rb#L262-L265 you now assign response_object to @body but not until after the after hooks have fired.

Is there a way for me to get at this?
Is there a reason I shouldn't?
Is there a reason @body shouldn't be assigned sooner?

Start with lib/grape/endpoint.rb around lines 262-265 and trace how response_object, @body, and the before/after hooks are ordered. Determine whether the after hook can expose the pre-JSONified response safely, then verify that the resulting response body and headers remain consistent.