Yes you can as long as:
1.- You can tight your Idle bearing to create enough pressure against extruder gear.
2.- Your filament is supported all the way in the extruder, if you have gaps the thinner filament might entangled in the gear.
3.- Your hotend have a true 2mm inner bore if all metal, if it have a PTFE liner might have no issues at all.
4.- Printing should be set at higher speeds and hotend needs to be cooled even if PEEK body.
