testrepo is full of completely separate VCS trees.
The standard approach is to:
create-project cwp/cwp-recipe-kitchen-sink
git init
git branch <my-version>
git remote add testrepo
git push
You may also wish to just re-use the last used branch, e.g.
git checkout cwp-2.5.1-rc1
git checkout -b cwp-2.5.2-rc1
rm composer.lock
rm -rf vendor
composer install
Just make sure that the composer.json is still correct before doing this