Not really; a reservation code is a reservation code regardless of whether fare class, seat assignment, etc. changes. The system could always allow the booking if the seat is adjacent, and enforce the adjacency if the child is of an age that requires it given they already know the age of the passenger. Far easier to handle with code than with human beings being told to execute a policy with 100% consistency, given they'll still get it wrong quite often and result in the same problem the human interaction was designed to solve, when code would not have permitted it otherwise.