I can't speak to the specifics of that printer, but rather than let you hanging without any sort of response...

On some printers changing the filament isn't a big deal - as simple as swapping out the hot end part of the extruder and adjusting some calibration factors.

The printer you're looking at is a Bowden extruder that has the extruder drive motor mounted away from the hot end, and the filament passes through a tube from the drive motor to the extruder. On that printer, you'd have to swap out the hot end, the PTFE Bowden tubing and fittings on both ends, and figure out what mods are necessary at the drive motor end.

Your preference for 3mm is interesting. Seems like most people prefer 1.75mm, arguing that there's a better selection from more sources. I'm not sure I've seen a price difference between the two.