Switching from GPS to Position Estimation

Hello everyone,

Is it possible while flying in Offboard mode (now only in SITL) to switch from external GPS to position estimation for a while and later switch back to GPS, or to cooperate with external position input with GPS signal. The need comes from flying to a place where GPS signal is not reachable or because of electromagnetic noises. Is it possible to make it without QG for example by MAVROS or MavLink (DroneCode)?