I don't know how maemo mapper works. If maemo mapper tries to reconnect periodically to the gpsd port (2947), you can turn minigpsd on or off anytime.

Maemomapper could itself start (and/or stop) minigpsd - it is just "/usr/bin/minigpsd", and "killall minigpsd" shell commands.

I'd recommend using the status bar applet. It has an indication of a lock (bluefill = off, redfill = starting, redcircle = not locked, greencircle (with sat dots) = locked).