I would probably recommend renumbering just 100 items at a time, over a weekend; until you have completed the project. 

I appreciate that but given we are running SQL these updates should be lightning.

I appreciate that but given we are running SQL these updates should be lightning.

The Sage 100 programming for the renumbering is the same for all versions (including Premium), where the programming goes through the data line by line.

I've considered writing custom SQL for renumbering projects in the past, but there are some brutal technical hurdles that scared me away after looking at what would be required.  The absolute last thing I'd want to do is corrupt the client data, and editing key fields is not something to be taken casually. 

My advice: use the Sage utility, running in batches (like StefanouM suggests).