The mods mechanism used in map editor is the same as in game.
To enable or disable mods
There is no button to start map editor directly from launcher, however you may use this approach to control active mods from any version of vcmi.
If you place any kind of objects from the mods, obviously, you need those mods to be installed to play the map. Also, you need to activate them.
You also may have other mods being activated in addition to what was used during map designing.
In the future, the will be support of mods versioning so map will contain information about mods used and game can automatically search and activate required mods or let user know which are required. However, it's not implemented yet