Hi VKUMAR,
No as per my knowledge you cannot activate it via standard settings at plant level, it gets activated at client level.
In OP5A you can make change number mandatory by marking it as a required field in screen group "PP task lists: initial screen". However then it would be mandatory at client level.
For your requirement you have 2 options as per me:
1) Create a screen variant for plant 15** and create roles for users of that plant that they always use your screen variant transaction and create routing with change numbers
2) Make change number mandatory by authorization only for users of plant 15**.
I believe you should discuss this requirement with your security consultant.
Best Regards,
Ameya B.