Query
How do I edit the Inventory Status Change page?
Findings
Upon checking, this is still a system limitation of NetSuite and currently, there’s an enhancement logged for this.
This is logged and being tracked under Enhancement: 591906 Transactions > Inventory > Inventory Status Change > Ability to Customize Inventory Status Change form
You can vote for this enhancement on the SuiteIdeas page.
At this time, there the only workaround for this is to hide fields using a Workflow. As for adding fields, I found out that the Custom Fields appearing in the Inventory Status Change are custom transaction body fields that are applied to Purchases, it looks that the Inventory Status Change record is under Purchases type record.