That is definitely not a recommended way to run 2.6 instead of 3.0 because there are also database adjustments that you definitely don’t cover.
If you already have a woocommerce shop and upgraded to 3.0 you can simply use your backup to get back to the old version…hopefully you are making backups before major releases.
If you want to start with woocommerce 2.6 instead of 3.0 simply download:
https://github.com/woocommerce/woocommerce/releases/tag/2.6.14
