I have not tried putting Express Edition on a server that already has Standard installed, but putting Express on first definitely works.
If you put another SQL edition on to a server that already has Express, nothing is changed regarding the Express instance.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
When I give food to the poor they call me a saint. When I ask why they are poor they call me a communist - Archbishop Hélder Câmara