Preferably if the employee flag field is not null I would like "XXXXX" or something similar to appear in the name field.
If you mean temporarily, then you cannot do this if the form field is bound, otherwise to do so would change the data in the table. You would need a duplicate of the name field, except the dupe would be unbound and the bound control hidden. The value in the unbound field would be altered by code.
If you are attempting to modify the appearance of data in a table itself, then that is what I'd consider to be the underlying problem since you should not be exposing tables to users or working on them directly as a matter of normal procedure. In that case, you might simply apply encryption on the field and decrypt (or not) in a form based on the value of your check field. At least that's my take FWIW.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.