From the paper Deep Blue by Murray Campbell et al (people who worked on Deep Blue) "The initialization of the feature values is done by the “evaluation function generator”, a sub-program which was run on the master node of SP system." Which would suggest it generated the heuristic itself. The features may have been hardcoded, but assigning values to them wasn't. In addition to this, feature values could be static or dynamic, meaning it would update dynamic ones depending on the board state. It not only generated the heuristic values (feature values) it could modify them to reflect their relative change in impact throughout the game.