League data may be edited at anytime after you have created your league. However there are few things you have to be careful of when editing league data.
Changing database names - You may change the names of all your databases or create new ones after your league has been created. Do not change a database name unless the new name is similar to the old name or has the same meaning.
Changing user-defined stat names - If you change the name of a stat you had defined before, you will more than likely have to change each players totals for that stat to zero unless the new stat title has the exact meaning as the old one. You also have to make sure any new stat will not interfere with a derivative stat you are currently using.
Changing game length - If you change the length of you games, the program will automatically use the new length to figure certain stats. You may have to reload any data in memory in order for the changes to take affect.
Be sure to Save your changes to disk before exiting.