How to use different versions of paraview python?
I would rename the old paraview.app to  paraview4.app and the new one to  paraview5.app.

Instead of exporting a path, create two aliases in ~/.bash_profile (and/or ~/.bashrc - it depends on if one sources the other)

alias pvpython4='/Applications/paraview4.app/Contents/bin/pvpython'
alias pvpython5='/Applications/paraview5.app/Contents/bin/pvpython'


If pvpython4/5 rely on the paths to /Applications/paraview*.app/Contents/bin/ I would choose a function which sets the path and calls the right binary.