Yes, you can. The sideloading method described in this guide does require root access. Simply uninstall updates for the current Play Store and install the older APK version.
The version number of the app he was looking for was 10.1.08. He tried to download it, but the Play Store wouldn't allow him. It kept showing him the latest version, 12.3.45. He searched online, but couldn't find any information on how to download an older version of an app. play store app download old version 10.1.08
To stop the Play Store from automatically updating to the newest version immediately: Yes, you can
Verified cryptographic signature matching original Google releases. Step-by-Step Installation Guide 12.3.45. He searched online