Advise on upgrading 150 spiders in the field to 4.2 from 4.1.8.0

Any advise on upgrading 150 spiders out in the field from 4.1.8.0 to 4.2 with IFU? Is it possible to upgrade just by deploying new clr.hex, clr2.hex, config.hex, app.hex and updater.hex?

I can imagine that 4.2.x.x has a new boot loader, how to deal with that in the field?

Any advise is welcome!

If you add your own hex files to the same folder as firmware, then it gets deployed by GHI Firmware updater as well.
Be aware that you need a .sig file to do so.
If you normaly work without sig files, you can create an empty key file with MFDeploy and sign your .hex files with it.

You must update everything at once. Including tinybooter.

This also may or may not work as this a major update. Going to 4.3 or more if future may not be a problem but 4.1 to 4.2 is questionable as IFU was rewritten.