Absolutely! This is one of the main features of magic-trace, and in fact a primary use-case.

You can select a trigger symbol for magic-trace to snapshot upon the next call of. This can be whatever you want, and you can imagine writing code like

  if (something_really_wonky_happened) { take_magic_trace(); }

and asking magic-trace to take a snapshot of the past only when `take_magic_trace` is called.