Fred,
For me it really was that simple. When I installed additional modules I just clicked the exe and was off. The setup wizard is really easy to go through and it might even already pull the correct database information during the installation(I can't seem to remember). The installation procedure will recognize what you already have and once it completes and you bring up the website you should see a tab with your new module.
Like you I have had a few issues with the website but running the config tool has fixed the issues. I even installed the IPAM evaluation on my main server for an evaluation and later removed when we decided not to purchase and I haven't run into any issues.
-Josh