An interesting question.
The MRPackages folder is part of the MrPI (Mobleread Package Installer) ;
Which is an extension to the KUAL menu.
Ah, but KUAL and MrPI are not **signed** update packages, just a document and some document data (from the Kindle's viewpoint).
So they can be "installed" without a jailbreak.
They will not run in the normal manner without a jailbreak, but this isn't a "normal manner" -
we don't know if it will work until you try it for us.
https://www.mobileread.com/forums/sho...d.php?t=225030
Get both KUAL and MrPI from the snapshots thread, un-archive into kindle:/documents
according to the directions for each. (The last link in each snapshot item is a link to the item's thread.)
Then try this method again.
Do not be surprised if it doesn't work, but be sure to let us know what happens.