We extend the model-updating method of selective sensitivity by employ
ing deliberate structural modifications. The resulting system-identifi
cation procedure reduces ambiguities in model-updating in two ways: by
augmenting the data base of the identification and by reducing the di
mensionality of the individual parameter estimations. It is shown that
deliberate structural modification allows selectively sensitive excit
ations with fewer actuators than in ordinary selective sensitivity. Th
e theory for choosing the structural modifications and the selectively
sensitive inputs is developed and illustrated with two examples. Forw
ard multi-hypothesis estimation is illustrated. It is suggested that t
he technology underlying smart programmable structures provides one me
thod for implementing the ideas developed here.