Pratta,
The simple answer is yes. However since you need a recurring task with a
moving period, the Insert/Recurring task feature won't help. You could
perhaps create a special calendar that only has the 4th working day of
each month available but that would be no easier than to manually enter
the task directly into the plan.
The process for creating the aperiodic tasks could be implemented via a
VBA macro. However, unless you need to insert a large number of these
tasks or need to implement them on more than one file, writing the macro
may take longer than simply entering the tasks manually. On the other
hand, if you feel a macro is the way to go but don't have VBA
experience, write me direct or give us a few more details on what kind
of task (i.e. milestone, tied to another task, etc.) you need and we can
help you get started.
John