Selective surface modification of bio-based fibers affords effective individualization and functionalization into nanomaterials, as shown by the TEMPO-mediated oxidation. However, such route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the full exploitation of the intrinsic supermaterial properties. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving spatially confined (regioselective modification of C6-OH) and dynamic surface functionalization. No polymer degradation or crosslinking nor changes in crystallinity occur under the mild conditions of the process and the modification is fully reversible, which offers a significant opportunity for the reconstitution of the interfaces back to the native states, chemically and structurally. Consequently, access to 3D structuring of native elementary cellulose fibrils is made possible with the same supramolecular features as the bio-synthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block.