Recommendation would be to use 8080f (non-ufi) as an intermediate code. Your upgrade path would look like this:
8070d > 8080f (non-ufi - same format as 8070d) > 8090d UFI (new file format - everything in one file)
Obviously not having console access is a downside should anything arise during the upgrade. That would really be your call on how critical the stack is to your business. I would not expect to have any issues, but you never know. If you would like assistance with the upgrade, I would recommend opening a support case.
Ben Beck, RCNA, RCNI, Principal Technical Support Engineer