I have CC2018 and CC2017 installed on my iMac running High Sierra. If I double click a CR2 file, Adobe camera raw opens and then I go into 2018. If I double click a PSD file, it opens in CC2017. I've tried associating the PSD file with Get Info but, it keeps reverting back to 2017. I removed the app for 2017 and associations fell back to CS6 and I still can't change the association. There is nothing that I tried that is allowing me to associate the PSD file with CC2018.
Somebody mentioned that removing CS6 in this thread fixed it and then they where able to install older versions again and the association stayed with CC2018