I think the question is: is there a way to populate a User::variable from an expression, eg. SET [User::variablename]='value' so that any subsequent expressions or SSIS tasks can read this value. That is, without using an independant script task to achieve this using VB.

A real world example: a single Send Mail notification task with multiple inbound Failure Precedents that knows the name of any given previous task because that previous task populated a User::variablename with it's own Task name. So the Send Mail subject line can be dynamically populated with the Task that failed.