Three observations:

(1)  Your description makes it sound like you're working directly in the
tables; if you want something to happen based on an "event," you'll need to
set up a form where you can write VBA code to evaluate your input to one
field and do x or y to a different field.  

(2)  Putting "completed" in a comments field is a poor solution, unless
that's the ONLY thing you use the comments field for.  Create an additional
field in that table (can be just a simple yes/no field) to store your
"completed" value.

(3)  Making some of the fields in your intake table "go to the main table"
suggests poor database design.  The whole point of having linked tables is
not to have the same information stored in two different places (the
exception being the key field you use to link the two tables together).