Changing a shirt after the Sabbath of Mourning
Question
Answer
If it is a shirt designated for the Sabbath, it is forbidden. If it is a shirt he usually wears on weekdays, he may remain with it after the Sabbath. This applies specifically to mourning for other relatives (brother, sister, son, daughter, and wife). However, if he is sitting shiva for his father or mother, he must tear this shirt as well, according to the law, on the left side down to the heart.
Source
The clothes are not considered special because they were worn on the Sabbath, but on weekdays a mourner is forbidden to wear Sabbath clothes, as explained in the Rema, Siman 389:3. Therefore, if he usually wears them on weekdays, he is permitted to continue wearing them after the Sabbath.
Regarding the obligation to tear, it is explained in the Shulchan Aruch, Siman 340:14: "For all the deceased, if he changes within seven days, he changes and does not tear. For his father and mother, if he changes within seven days, he tears all the clothes he changes and never mends, as the first time."