Most electronics are insensitive to magnetic fields from these magnets, which are pretty localized. For example, R/C planes often use magnets to hold hatches on right next to their receivers and ESCs. Exceptions would be anything that senses magnetic fields deliberately, like magnetic apogee detectors. I'm not seeing how moving the magnet would cause the BPC to come off, though, at least not during boost, since it would still be held on by aero forces. I've long thought about a staged Little Joe II but I wouldn't try it on a model this small.