I'm brand new on the forum, so thanks for all the help I already found there.
I'm planning on replacing my standard CR10S PRO V2 extruder with the Hemera. In parallel, I'd like to get to OctoPi. Has anyone built such configuration and could give me an insight about it and how difficult it would be to configure? Maybe even have a rough procedure? I don't really want to make the investment if it is not possible, as I don't know OctoPi enough to tell.
Installing the Hemera extruder is going to require either the use of custom firmware for your 3d printer, or adding custom Gcode at the beginning of the print so that the extruder is correctly calibrated (so on the slicer settings), but there's nothing you'll have to do on octoprint's side.
No, OctoPrint (& the preinstalled OS for Raspberry Pi OctoPi) just commands the printer what to do over the USB port, it's widely compatible with most common firmware, though you will have a better experience with firmware that does not have loads of bugs like Creality's...
Whatever firmware you use, you will probably need to make modifications to the source code to support the new extruder. That means you will need the ability to build the firmware from sources.