Overtype value in form and create new record in table

[Snowsride]

I have a table that stores records that each have an effective and inactive
date. A current record has a null inactive date.

I want a form that shows the current values for each record BUT I want the
user to be able to overtype the displayed value and then save the record.
When the record is saved it should set the current record's inactive date to
sysdate and create a new record with an effective date of sysdate and a null
inactive date.

Help appreciated.