Collectible Card Game Headquarters

How can I import a Custom Set, such as a Cube? Will it work for sealed and drafting?

On the server, sure, simply create a deck file and save it as .cube

Make sure the file's first two lines are:

// NAME: <cube short name>
// DESC: <cube description>

Where <cube short name> could be something like CUB1 and <cube description> could be any description

Place this file, say mycube.cube in .\data\games\mtg\ folder.
Restart server or press reload cubes under sealed.

Now on the server you can use the cube like it were a set.