WordNet sense 1 (a minor actor in crowd scenes):

supernumerary, spear carrier

WordNet sense 2 (something additional of the same kind):

duplicate, duplicate

WordNet sense 3 (added to a regular schedule):

special

WordNet sense 4 (not scheduled or not on a regular schedule):

unscheduled

WordNet sense 5 (more than is needed, desired, or required):

excess, redundant, spare, supererogatory, superfluous, surplus

WordNet sense 6 (not necessary):

unnecessary, unneeded

WordNet sense 7 (further or added):

additional