Ingame content is managed through a web interface called FWN. Changes can be made by any player, to almost anything ingame, and updates are live immediately and with no restart required.
Info: We're still on a case-by-case manual approval process for write access. To get write access, you will have to talk to niv. Once you have access, you can start uploading content - and everything will be live ingame immediately, no restarts required.
More Info: By default, new authors are only allowed to upload areas (.are, .git) and dialogues (.dlg). All other templates (interchangably called resrefs, files) are restricted to those maintaining shops, encounters, and so on and are not needed for area updates.
It is strongly recommended to read the proper article pertaining to the changes you want to make. For example, if you want to work on a new or existing area, check out Areas before getting to work. Nearly all maps have a "maintainer" - someone responsible for the general feel for things, and what should happen to it in the future. It's best to talk to them beforehand.
If you have any questions, post here in the comments or contact niv directly.
Now, FWN may look daunting at first glance, but it's really not. Let's go through an example on how to edit a area. The general workflow is very simple:
Commit is simply means "Apply the complete uploaded changeset and record it".