Carboxylic acid groups introduced in cellulose by various oxidative pre-treatments (purification, dissolution) can massively influence materials' properties motivating research on counteracting conversion schemes. We used cellulose thin films to unravel the patterns of different intra- and intermolecular esterification reactions. The impact of the formation of ester bonds on the charging and swelling was studied by streaming potential/streaming current measurements and in situ ellipsometry. Methylation was found to result in a slightly reduced swelling and ion conductivity of the cellulose layers. Self-esterification reactions caused higher degrees of conversion of the carboxylic acid functionalities producing a dramatically altered swelling and ion conductivity pattern. "Carbodiimide-activated" induced self-esterification was found to be more efficient than any thermally induced conversion. Together, our study quantitatively shows the potential of self-esterification protocols for the modulation of performance-related characteristics of cellulose materials.