When a playlist is on air, it is still possible to apply some changes on it, as "insert", "modify", "delete", "replace".
However, for security reasons, any modification on the item which is on air is impossible.
Playlist modifications are done from the "On air Follow-up" tab, but also from a planning workstation where the "Federall" tab is installed.
Attention : To modify a playlist from a planning workstation, you must have the rights.
Moreover, if a playlist is modified, the "notification" icon is flashing 
.