122:16 We have wrote above, in 122:9, that one may wear freshly-laundered undergarments and socks on Shabbos Chazon because they are worn primarily to absorb sweat. When it comes to the rest of one’s Shabbos clothes, it all depends on the accepted local practice. In the shul, the curtain of the aron is changed, as are the table covers and the mantles of the Torah scrolls. This is done on Shabbos Chazon, but not when Tisha b’Av falls on Shabbos. (Mishnah Brurah 551:6 says even when Tisha b’Av falls on Shabbos.)
122:17 It is customary on Shabbos Chazon to call the rabbi for maftir because he knows the mournful tune, rather than for the third aliyah as usual.