inserting own php code into DMX code

I am slotting a bit of php (its a mail() so that the form values are sent to
an email address as well as going in the db) into the $editFormAction which
includes an Insert Record Server Behaviour.
On "Save", it tells me that the Server behaviour has only been partly
deleted, so I went and recreated it.
Now I have TWO Insert Record Server Behaviours (in the code, its not visible
in the right hand panel) which of course adds two of everything to the db.
Ok, so next I delete the extra Insert... so that just the $editFormAction
with my bit of code is still there, save it and the Server Behaviour has
changed from a Insert Record to a Dynamic Attribute.
They both work (apart from the double save to db) but I was wondering if
there is a better way of doing this and how you change the Dynamic Attribute
when needed?
Andy