The present invention relates to post-treatment compositions and methods useful for modifying the distribution of metal biocide(s) in biodegradable substrates such as wood, other cellulosic products, starch-based products, and the like that are vulnerable to decay due to insects, fungi, microbes, and the like. The compositions include complexing agents of moderate strength that are able to facilitate mobilization and redistribution of metal biocide(s) in substrates without undue leaching. The compositions can be used, for example, to redistribute the metal biocide(s) into depleted regions of a substrate by redistribution of metal biocide from other regions of the substrate. Post-treatment compositions that include additional metal biocide can also replenish these regions with the freshly supplied, additional biocide. Thus, the depleted regions can be restored by redistribution and/or replenishment mechanisms. Service life of substrates in the field benefits by these post-treatments as a consequence.