The recent advent of integrated waveguide systems with reconfigurable propagation constants and coupling coefficients has opened the door to using waveguide detuning as a resource for readily tailoring the quantum properties of light states. Here we theoretically demonstrate that waveguide mode detuning can be used for molding the nonclassical properties of two interacting quantum optical fields in integrated waveguide couplers. In particular, we explore the states that are generated by conditional measurements when one of the input ports of the waveguide coupler is excited by coherent states, squeezed vacuum states, and thermal states, while the other port is excited by a single-photon Fock state. We explore the detuning range required to attain nonclassical states. Our findings could pave the way for a robust integrated-optics protocol, providing enhanced control and engineering capabilities over multiphoton quantum states.