Hi Yathan,
You can control the validity dates of lead change number and at the item level number as will using configuration.
SPRO -> Logistics - General ( follow below path)
For a selected ER type, below screen shows tell you when you want system to create a lead change number at what status.
Here you can map the 'target date' to 'valid from' at the header level like below or any header ER attributes.
Similarly at the item level, you can define what status change number to be generated and what attributes of ER to be mapped.
if you need more flexibility you can use below standard BAdi
Hope this helps.
Amar.