How can I stop a single Progress OpenEdge server process and not the whole database?
After googling around some more with different queries, I found my answer from the Progress Knowledge Base after all.

First of all, it turns out that indeed, the remote server processes by default stay active until database shutdown happens. So if all the slots are occupied by 4GL servers, they will not open up a slot for a SQL server by themselves.

However, the PROMON utility has commands to terminate specific server processes gracefully to free up server slots. The sequence of commands is as follows from the PROMON main menu:


R&amp;D for Advanced options
4 for Administrative functions
7 for Server options
7 for Terminate a server


From the server list find the server ID that needs to be terminated and type it in. After issuing the command, using the R option to refresh the screen the terminated server ID should show up as inactive.

After terminating a server, a new SQL server should be spawned if an ODBC connection to the system is initiated.

On Windows you might need to use a local user account, that is in the Administrators group. Domain users belonging to Administrators group are not allowed to terminate servers.

Sources:


Background information how remote servers are handled
Instructions on how to terminate a single server process
Information on how domain administrator accounts are handled on Windows