Can I safely downgrade an encrypted Asus Transformer TF101 from 8.6.5.21 to 8.6.5.19? I want to root my encrypted Asus Transformer TF101 (Firmware 8.6.5.21; Serial B80...) and install a custom ROM. I read that the only way to do this is by downgrading to stock 8.6.5.19 and then using Razorclaw. 

I know that using tablet encryption with Custom ROMs is a big no-no, so I will have to wipe my data (factory reset). However I do wish to keep some application Data (such as save games) to which I only have access via root. 

So my question is, can I: 


Safely(!) downgrade to 8.6.5.19 on my encrypted tablet
root
backup
unencrypt the tablet (factory reset)
install custom ROM


or do I have to: 


factory reset (losing all my precious data)
downgrade to 8.6.5.19
root
install custom ROM


Update:
I found out that Asus already includes an app which allows to save application data without root (aptly named "App Backup"). So I will go with the second option. I'll leave the question open though as I still don't know if I could have downgraded without doing a factory reset.
I ended up doing a factory reset on my tablet (after doing a backup of my data with "App Backup"). As far as I know the downgrade would probably have worked, but I decided not to risk it.