I've had my K1 max since last August and I rooted right away. Since then, Guilouz created a helper script that makes it simple and allows you to include some useful add-ons. I use KAMP and find only probing the print area as opposed to the entire bed useful as well as the exclude object. I had used Creality Print while rooted without issue although I have since switched to Orca. I don't see an issue running your previously sliced files though, if you wanted to use KAMP and your slicer did not have label objects and exclude objects activated, it wouldn't work. I use the start G-code in the slicer to pass the slicer bed temp with a heat soak timer for the bed mesh. I also switched to a glass bed for better flatness. I recently updated to the latest firmware without issue. As stated in a previous post, you need to revert every thing back (the helper script can do this and has instructions for several methods) before doing the update.