I wanted to make note that if you want to set values to variables one way to do this is via the sql job. You do this in the Set Values Tab (job properties, step properties, set values tab).
Set the property path to your custom VARIABLE_NAME
\Package.Variables[User::VARIABLE_NAME].Properties[Value]
Set the value to your custom value. The advantage of doing this, of course, is being able to dynamically change a value instead of changing the source. For example, I like to set up email messaging here instead of hard-coding inside the application:
Property Path:
\Package.Variables[User::EmailErrorsTo].Properties[Value]
Value:
user@company.com
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