Can central heterochromia eventually expand to sectoral or complete heterochromia?

While central heterochromia can be a stable trait, it's unlikely to spontaneously transform into sectoral or complete heterochromia over time. These different types of heterochromia are usually determined by genetic factors during eye development and remain relatively stable throughout an individual's life. The specific patterns of iris pigmentation depend on the distribution and expression of melanin, and changes in these patterns typically occur during early childhood and stabilize thereafter. It's very uncommon for significant alterations in iris pigmentation to occur later in life unless caused by certain medical conditions affecting the eye.