Hotend on a Neutron printer: E3D vs MK8
Yes, but...
Technically, you can reuse your old heater block and nozzles and just buy a new heartbreak and cooling body or the other way around. However, you might run into problems under working conditions, especially if you install the heater block together with its native heating cartridge and thermosensor. Installing a thermosensor to which the printer is not adjusted to can lead to all kinds of problems - Firmware update is a must!
Another source of trouble could stem from not taking care in the change itself. The Makerbot MK8 seals the hotend by pressing the liner against the nozzle, which itself is seated against the heartbreak, just like the e3D lite6 seals itself. On the other hand an all-metal e3D v6 seals itself by seating the heartbreak against the nozzle on a larger area. If the seal is imperfect, the Makerbot Mk8 style tends to leak out through the top. Such a leak can leave plastic in the threading which has to be removed carefully before reusing.