Is it practical to build a separate hotend temperature controller to assemble hotends without taking up printer time? One could make such a controller with 3D printer parts and building a case for them, but is it significantly less than just buying a compatible low-cost printer.  The intent is to heat up the all-metal hot end to tighten the nozzle to the heater break.
You can get a suitable board for $20 or so, print a case for a few cents, and either repurpose an old PC power supply or buy a new one just powerful enough for the hotend (not bed) heater very cheap, so I think it's a lot less costly than a cheap printer, and cobsumes less space. But I'm not clear what you need it for.