Reconfiguration of a wavelength routed optical network with the aim of minimizing congestion results in establishing lightpaths between node pairs having large traffic and tearing down lightly loaded lightpaths. Applications such as grid computing, e-science, three dimensional (3D) teleconferencing consume large bandwidth and require that the lightpaths are available for the entire session although there might be intermittent periods with less traffic between the nodes. Hence, the reconfiguration process must not tear down these lightpaths. We propose a qualitative heuristic algorithm in which lightpaths are assigned priority according to the class of traffic, and the lightpaths of high priority applications are not disrupted by the reconfiguration process. For low priority applications such as email, when the lightpath connecting the nodes is torn down, the data can be transmitted by multihopping. Extensive simulation has been carried out and it is shown that reconfiguration of the network can be carried out without disrupting the lightpaths of high priority traffic and also not affecting the network performance considerably.