I'm new to sage, and have a customer that wants to upgrade from 4.5 to 2017. I'm doing some reading of the documentation, and it mentions pre-migration and parallel migration utilities, converting the data to 2017, and migrating it to 2017 version. My assumption is that once I work through that pre-migration data conversion, the existing 4.5 system will be unusable? Is there a way to do a "test run" migration? Would backup/restore of the MAS90 folder help, i.e. backup the folder, do the data conversion and migration to the new, restore the old MAS90 folder so users can still access production system while testing the new in parallel? Thanks for any insights you can provide.