Is it permissible to lengthen the eyebrows in the event that half of them were plucked in childhood, leading to the forehead appearing larger?

It is impermissible to lengthen eyebrow hair for the purpose of adornment. However, if it is considered a disfigurement or a defect, then it is permissible to lengthen them to the extent that removes the defect. This is because removing a defect and restoring something to its natural state is not considered altering Allah's creation.