You need to add a workflow that changes the record type when the record needs to be locked. You can then use different page layouts for each record type.
Option B
Your validation rule needs to use ISCHANGED to detect if the field has been edited. The user will be unable to save the changes to the Amount field.
Option A
You need to add a workflow that changes the record type when the record needs to be locked. You can then use different page layouts for each record type.
Option B
Your validation rule needs to use ISCHANGED to detect if the field has been edited. The user will be unable to save the changes to the Amount field.