Can I install SQL Server 2012 Express edition on a same machine with 2012 SQL Server Standard version As I would like to say that we are going to downgrade the SQL Server Standard 2012 SP1 edition with SQL Server Express 2012 SP4 in one Production Server.

For the time being I want to keep the SQL Server Standard 2012 SP1 in that server and I want to install the SQL Server Express 2012 SP4. Until unless the SQL Server Express 2012 SP4 will be not come to production. Till time I want to keep the SQL Server 2012 Standard SP1.


  My Question is that at the same time can I install the SQL Server
  Express 2012 SP4 along with the SQL Server Standard 2012 SP1 in the
  same Server.


Note : Suppose that as the Running SQL Server 2012 Standard SP1 instance name is ABC. Can I install the same instance name (ABC) of SQL Server 2012 Express SP4 or it will be different.
Suppose that as the Running SQL Server 2012 Standard SP1 instance name
  is ABC. Can I install the same instance name (ABC) of SQL Server 2012
  Express SP1 or it will be different.


You cannot have two named instances of SQL Server with the same name on the same pc. 

So your options are 


first uninstall your first instance and then install the second and
use the old name for newly installed second instance
give the second instance different name, but you can then alias it
with the first server's name once you uninstalled the first server


Here you can find information about aliases