In Avalanche Attack Designer, you can open an existing threat in the attack database (i.e. synflood2.xml) and make some modifications. After the modifications you can Save the new attack in the Attacks directory of your pc.
In case you see an error message like the following:
You need to uncheck "Enhanced V3.0 Threats" from Preferences:
After that, you'll be able to Save your threat. The above feature is not used anymore from the Attack Designer.