Pause the print at layer 18 (with 0.2 layer height) or 3.60mm height and insert a 20mm x 3mm round magnet, 3mf already contains a pause at the correct height.
I used ferrite magnets and they stick just fine on a fridge, you can use neodymium if you want it to be a stronger magnet.
Buy Magnets:
UK: https://amzn.to/3IPekbq
US: https://amzn.to/3xMZH1T
You should double side tape your magnet into the cavity if you have any magnetic parts on your print head assembly, it may cause damage to your 3d printer if the magnet is lifted during the print.
I have also included an stl file without the magnet cavity so you can remix for different size magnets, or you can print without magnet as a toy or garden ornament.
The purple ladybirds were printed with X1C+AMS in 2 colours the remaining images were painted by hand after printing in a single colour.