In Esther 8:15 Mordechai goes out wearing royal clothing again. This seems to be a singular reward; what precipitated this?
it is the same set of royal clothing in both psukimm in between these two periods, mordechai put back on the sackcloth (talmud:megilla) due to the jews being under threat
only when the threat was removed did he remove the sackcloth and wear only the t try oy all set (manos halevi,gri”z)
this (start from 46:50), based on the meam loez, says that he also had Tzittzit and tefillin so that every one would know that, The One in Power now is a jew.