Ah, I assumed you wanted the Standalone installations (mac app bundles in the dmg files and windows setup.exe files)
If you want to install in your own Python environments then yes, you can do pip install.To install particular versions of software with pip the standard command is:
pip install psychopy==2020.1.2
I’m also quite wary though of different pythons being installed and often the pip doesn’t match the thing that is called by callnig ‘python’ so I often do
python -m pip install psychopy==2020.1.2