These guys suggest orbital "changes" are the reason that gas giants have been found in very close proximity to their host stars.
"we might expect any planetary system to follow the general plan of our own, with small, dense, rocky worlds occupying orbits close to the central star and large, low-density, gassy worlds orbiting at much greater distances. However, the majority of the first batch of extrasolar planets to be confirmed do not conform at all to this scheme. Planets with masses even greater than that of Jupiter have been found in near-circular orbits within 2 astronomical units (and, in some cases, within 0.1 AU) of their host stars."
Perhaps the concept of changing from one stable position to another isn't necessary. One can just envision a decaying orbit.
Perhaps Global Warming is just orbital decay.