No because WSUS bundles your data together and digitally signs it - but there is an easy way to review it for a superseding update/new update:
- Revise your old package, left click the ID link and look in the GUID folder for the action file.
- Pull it out and edit it with a colorized editor like notepad++/Sublime/atom. OR Open up a new Custom Update window and mimic your changes OR edit the action file by hand.