you need to set up a new profile on cura for the petg,
also as petg will be used at a higher temperature than pla you need to clean out the nozzle after use.
this consists of
- doing your print
- removing the petg
- insert pla into the machine (still on the petg settings)
- manually extrude for 10 seconds ,wait for 5 seconds (repeat 4 times) or run a small 2-3 minute print with pla but on petg settings.
- remove the pla.
and yes the new ruby nozzle means carbon fiber can be used