I did magnetize the arms and tail of my Trygon/Mawloc, and painted all the optional pieces. Below you can see pictures of a few of the possible configurations.
It's a little difficult to get the arms in a position that works well. The top two sets of arms are positioned very close together, so they can get in the way of each other. And the top set of arms gets tangled up in the many spines coming off the head, so there aren't many options for where to position that set. But with the five different sets of arms, I'm sure I can come up with options that work okay.