Block field update for the first entered value

The issue: When the desired field don't have any value, and some data have been added there, no matter from where they come -> Marketo keeps the first introduced value.

We were wondering if there is any possibility to block first entered value into the field.

Purpose: Basically, we would like to achieve the next scenario when assigning the first value to a field.

Initially, this field has "NULL" value, and when assigning the first value to a field it should not allow/enter/save it.

Marketo: ========> Marketo (after updating the page):

"Field X" -> "test" ========> "Field X" -> "NULL".