I've done a large amount of upgrades, and experience taught me this very important lesson: if you miss one step in an upgrade procedure (you should prepare this because every release is different), you'll run into problems. So if Cisco says it's not supported, I'd say believe them, and don't try to. It might not be obvious on the outside, but the database structures change a lot, so it can cause a lot of corruption should the installer let you do the upgrade.
There is no way this will work as there are features in CM 4.2 not available in 5.X, alos some entities such as Device Pool are restructured with different fields which means that the DB is different. I dont see how this would be possible without upgrade tool aware of the differences.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...