In the mod folder there will be 3 subfolders, About / Assemblies / Defs. Inside the About folder is an XML Document named "About". Edit this in notepad and change the <targetVersion>0.18.1722</targetVersion> to have the A17 or A16 version number. Version number can be found in the top left corner in the Rimworld main menu. Also copy this now edited mod into the Rimworld/Mods otherwise the workshop will change it back to B18.