Measurement Update as Operator Reclassification: A Regime-Conditional Account (IM-E005, v0.3)

This document is part of the Informational Mechanics (IM) framework and is published in the IM-E (Measurement & Operators) series within the IM v0.3 corpus. The paper analyzes quantum measurement update as an operator reclassification problem under admissibility constraints. Rather than introducing collapse dynamics or new axioms, the analysis formalizes the structural conditions under which outcome weights are uniquely determined by orthogonal additivity, invariance, and minimal regularity requirements. Building on the mathematical uniqueness result of IM-B002, the paper shows that admissible strength functionals compatible with operator-defined observables must take the squared-norm form within quantum-mechanical regimes. Measurement update is treated as a regime-bounded representational transformation rather than an ontological discontinuity. The work introduces no new axioms, collapse models, hidden variables, or empirical fits. Its contribution is operational and classificatory: it clarifies the admissibility conditions under which squared-amplitude outcome weights retain scientific meaning while preserving unitarity and operator-defined locality.