Is it possible to run multiple Python versions on SQL Sever 2017?
It is possible to do on Windows (2 Python folders, 2 shortcuts, 2 environment paths). But how to launch another Python version if I run Python via sp_execute_external_script in SQL Management Studio 18?
In SQL server\Launchpad\properties\Binary path there is the parameter -launcher Pythonlauncher. Probably, by changing this, it is possible to run another Python version.
Other guess: to create multiple Python folders C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\PYTHON_SERVICES. But how to switch them?
Other guess: in C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\MSSQL\Binn\pythonlauncher.config - in PYTHONHOME and ENV_ExaMpiCommDllPath parameters substitute the folder C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\PYTHON_SERVICES\ with the folder with new Python version.
The answer is:

Copy in 


C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\

folder as many Python versions as you want (Python version = folder with Python like PYTHON_SERVICES)

Stop Launchpad
Change in 


C:\Program Files\Microsoft SQL
  Server\MSSQL14.MSSQLSERVER\MSSQL\Binn\pythonlauncher.config

file: in PYTHONHOME and ENV_ExaMpiCommDllPath parameters substitute the folder 

C:\Program Files\Microsoft SQL
  Server\MSSQL14.MSSQLSERVER\PYTHON_SERVICES\

with the folder with new Python version.

Start Launchpad
Run multiple python version on SQL Server (2017)