In a visual light communication (VLC) or other light based positioning system, a mobile device can detect modulated light emitted by one or more localized artificial lighting devices to obtain an identification (ID) label or code of each lighting device, e.g. that is visible in an image captured by the mobile device camera. The mobile device uses the detected ID code for a lookup in a self-stored or remotely stored table that associates light-source-location information with ID codes, to obtain an estimate of mobile device position. To mitigate against hacking by a third party detecting the ID codes and observing locations to compile its own lookup table, the disclosed examples dynamically alter the assignments of particular ID codes to the lighting devices, while minimizing potential disruption of position determination service for mobile devices due to the changes to ID code assignments.