Status Network set up for Inbound pdf. docs in CG50?

Hello Experts,

I have a client requirement, acc. to which an Inbound vendor MSDS should be uploaded as a pdf. to the EH&S report tree. After that, the uploaded MSDS should pass a review and approval process containing three steps, before being released.

Have you been able to build a review and approval flow for uploaded external report documents? In CG50?
E.c., the report to be reviewed and approved is an external pdf., so the report content does not derive from EH&S report tree.

I use the IBD doc type (a pdf.), and the upload transaction CG36VEN. This transaction allows he upload only with a Generation Variant that is set into a "Released" status. The next status after "Released" is "Historical" and in between these two statuses, it seems not possible to insert any additional statuses.
Is there a way to change Gen Var. default status for the inbound documents and build a status flow?

Another question, related to this issue: in the transaction CG2B, where does the Generation Variant pick the Status selection list from?
Can this list be modified or extended in SPRO and how?

Many thanks in advance for your input!