How to change settings in a middleware?
No, there is no way to do this, and that's a very good thing as it is a bad idea. There is no reason to use the same Apache process for different sites: instead you should have different virtual hosts for each of your sites, and let Apache manage them.
I'd like to change the environment variable DJANGO_SETTINGS_MODULE (along with a few others) and then have ALL relevant modules like django.conf, django.db etc reloaded to reflect the information from the new settings module. The new settings module will have different database. I will be doing this in a middleware.
I was able to achieve this by reloading a few modules along with django.conf and django.db. All new SQL statements were fired against the new DB.
But this appears to be so hackish. 
The main reason for me wanting to do this is to have the same apache child process serve requests for different django applications (different settings and not different apps) without having to recreate a new apache child process which reloads the whole thing.
Is there a clean way of achieving what I want to do?
Thanks,
UPDATE (19-Sept-2014): I have accepted Daniel Roseman's answer as that seems to be the reality in the context of the question asked. The Router approach suggested by him was something that I explored but couldn't use because django's transaction classes don't use the router. The router I presume exists for a different reason. The application code base I'm working on, which is pretty large, has tons of transaction.commit_manually for the default or a specific db alias. I was trying to get this to support multiple client databases without changing the application code.
However, I did manage to solve the main problem which was to support multiple client DBs and other settings. I don't try to change the settings on the fly nor do I use the router. I instead have a single settings.py with all client DB information. I monkey patched the connection handler to return a different database connection for 'default' alias (or other specific alias used by the code) based on certain env variables set in the middleware. So far this has worked fine. I will post an update if I run into any issues or if someone else can point out a potential issue with the approach.