Functional and sensory augmentation of living structures, such as the human skin and plant epidermis, offers vast opportunities for biology-machine interface, wearable health, and environmental monitoring. However, current sensor and electronic formats could be obstructive to their hosts’ inherent sensations or physiological changes. Challenges are also faced in widening the augmentation of living structures without drastically increasing the global environmental and ecological burdens. Here, we demonstrate imperceptibly augmented living systems, through in situ tethering of poly (3,4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT:PSS)-based organic bioelectronic fibres. Customising fibre tether patterns and modalities enable applications from biopotential acquisition and skin-gated organic electrochemical transistors, to augmented touch and plant interfaces. The open networks formed by the intrinsically substrate-free fibres provide a biomorphic interface, while supporting direct coupling with microelectronics and e-textiles. We further demonstrate conceptual fibre formats for on-demand device repair, upgrade, and recycle, or for enhancing electromechanical stability against touch. Our work may unfold wearable technologies that are simultaneously biologically-adaptable and sustainable.