Eden Editor: Custom Composition
Apart from pre-defined groups and compositions, you can save and share your own.
To save a composition, select the entities in the scene, click right mouse button on one of them and pick the Save Custom Composition option (or use the 
button in the Asset Browser).
A window will be opened where you can set a title, author and category for your composition.
In the list on the left, you can either choose to create a new composition, or overwite one of the existing ones. This way, you can edit already created compositions.
Once created, you can find your compositions in Compositions > Custom. Place it just like any other entity - either select it and then click in the scene on desired position, or drag it from the list to the scene.
Terrain Level - composition will be snapped to the surface underneath. Please note that objects which are placed on another objects may no longer be positioned precisely.
Sea Level - the composition will be placed exactly as it was saved, ignoring surface slope. This option may work better for complex compositions, especially when manually lowering the entities after placing.
To edit a composition's attributes, double-click on it, or select it and click on the Edit button (or use the 
button in the Asset Browser). It will open a window where you can change the title, author and category again.
In order to delete a composition permanently, select it in list and then use the 
button.
Publishing Compositions
You can also publish your compositions to Steam Workshop. Do so by selecting the saved composition in the Asset Browser, and then using the 
button there.
A publishing window will be opened where you can enter a name, description, visibility setting, image, and various tags. After agreeing with the Workshop license, you are free to publish the composition and share the link with others.
Republishing Compositions
Updating a composition that was already published is effectively the same as the first time. Select the composition and use . In the publishing window, select your already published composition on the left. Consider entering relevant change notes and publish.
Unpublishing Compositions
In order to unpublish a composition from within Eden Editor, open the publishing window by selecting any saved composition and using the button. Now select the published composition in the list on the left and press DELETE.
Subscribing to Compositions
You can easily find all published compositions made by yourself and others by selecting the Steam subscribed content entry in the Asset Browser, and then pressing the button. This will open a Steam overlay with the Workshop opened and compositions filtered. Soon after subscribing to any number of composition items there, the game should download these in the background. They will then be listed in the Asset Browser, ready for regular placement. Note that large compositions may take a brief while to download and appear.
Unsubscribing from Compositions
To unsubscribe from a Workshop composition from within Eden Editor, select it in the Asset Browser and press the button. Note that you should look for compositions listed under Steam subscribed content, otherwise you may accidentally delete a local composition instead.
Local Files
Compositions are saved in the Compositions folder in your Profile directory.
They can be shared freely - if you pack a composition folder into a *.zip file and make it available for download, people who place the unpacked composition to their Compositions folder will have it available as well.