First of all, it is a bit odd to talk about specific plans. If you think about emergency procedures for other natural phenomena, such as Hurricanes or Earth quakes, you need to keep in mind that a reversal is a long-term process which is supposed to take decades to centuries. This is what is called geological time scales. In a way, some scientist say, that the "next" reversal has already started. For proving this statement, scientist usually refer to the current characteristics of Earth's magnetic field. It is somewhat different from a "clean" dipole, which it is supposed to be according to basic physics.
Since the process of Earth's magnetic field's reversal was first simulated by computers, it has been agreed on that the overall field strength (around 50µT at the Earth's surface) will not drop significantly. For further reading, have a look at the ground-breaking work of Gary A. Glatzmaier, Paul H. Roberts et al. A three-dimensional self-consistent computer simulation of a geomagnetic field reversal, Nature, 1995.
Talking about space exploration in this context, there are plenty of missions which relate to this issue. First, you need plenty of data / observations of Earth's magnetic field for understanding it (and for tuning & verifying the computer models). Second, you need monitoring of the field with respect to sudden changes. Sudden changes may only be caused by solar activity, so from a scientific perspective, such missions actually monitor the solar weather.
But talking about plans and although such sudden changes should not trigger a reversal on their own, those effects account for most problems here on Earth with respect to Earth's magnetic field. The most prominent example is the geomagnetic storm of March 1989, which had significant influence on the power grid in North America. Although there have been improvements to e.g. power grids, to the best of my knowledge, there is no overall plan of how to handle a massive solar storm (thus a massive change in Earth's magnetic field) in most countries. The space probes at the Earth-Sun-system's Lagrangian points remain the first (and last) line of defence (for early warning) against such events.
Notable missions for looking at Earth's magnetic field: Magsat, Ørsted, Swarm.
Notable missions monitoring solar activity: STEREO, International Sun/Earth Explorer 3 (ISEE-3), WIND, ACE, SOHO.