Here's what will be airing on Comedy Central on April Fools' Day, all times Eastern:

6am-South Park: "Ike's Wee Wee" (S2E3, OAD: May 20, 1998)
6:30am-South Park: "Conjoined Fetus Lady" (S2E5, OAD: June 3, 1998)
7am-South Park: "The Mexican Staring Frog of Southern Sri Lanka" (S2E6, OAD: June 10, 1998)
7:30am-South Park: "City on the Edge of Forever" aka "Flashbacks" (S2E7, OAD: June 17, 1998)
8am-South Park: "Summer Sucks" (S2E8, OAD: June 24, 1998)
8:30am-South Park: "Chef's Chocolate Salty Balls" (S2E9, OAD: Augst 19, 1998)
9am-South Park: "Chickenpox" (S2E10, OAD: August 26, 1998)
9:30am-South Park: "Roger Ebert Should Lay Off the Fatty Foods" (S2E11, OAD: September 2, 1998)
10am-South Park: "Clubhouses" (S2E12, OAD: September 23, 1998)
10:30am-South Park: "Cow Days" (S2E13, OAD: September 30, 1998)
11am-South Park: "Chef Aid" (S2E14, OAD: October 7, 1998)
11:30am-South Park: "Spookyfish" (S2E15, OAD: October 28, 1998)
12pm-South Park: "Merry Christmas, Charlie Manson!" (S2E16, OAD: December 9, 1998)
12:30pm-South Park: "Gnomes" (S2E17, OAD: December 16, 1998)
1pm-South Park: "Rainforest Shmainforest" (S3E1, OAD: April 7, 1999)
1:30pm-South Park: "Spontaneous Combustion" (S3E2, OAD: April 14, 1999)
2pm-South Park: "Tweek vs. Craig" (S3E5, OAD: June 23, 1999)
2:30pm-South Park: "Jakovasaurs" (S3E4, OAD: June 16, 1999)
3pm-South Park: "Sexual Harassment Panda" (S3E6, OAD: July 7, 1999)
3:30pm-South Park: "Cat Orgy" (S3E7, OAD: July 14, 1999)
4pm-South Park: "Two Guys Naked in a Hot Tub" (S3E8, OAD: July 21, 1999)
4:30pm-South Park: "Jewbilee" (S3E9, OAD: July 28, 1999)
5pm-Family Guy: "Bookie of the Year" (S15E2, OAD: October 2, 2016)
5:30pm-Family Guy: "American Gigg-olo" (S15E3, OAD: October 16, 2016)
6pm-Family Guy: "Inside Family Guy" (S15E4, OAD: October 23, 2016)
6:30pm-Family Guy: "Chris Has Got a Date, Date, Date, Date, Date" (S15E5, OAD: November 6, 2016)
7pm-Family Guy: "Hot Shots" (S15E6, OAD: November 13, 2016)
7:30pm-Family Guy: "High School English" (S15E7, OAD: November 20, 2016)
8pm-Family Guy: "Carter and Tricia" (S15E8, OAD: December 4, 2016)
8:30pm-Family Guy: "How the Griffin Stole Christmas" (S15E9, OAD: December 11, 2016)
9pm-Family Guy: "Gronkowsbees" (S15E11, OAD: January 15, 2017)
9:30pm-Family Guy: "The Dating Game" (S15E14, OAD: March 5, 2017)
10pm-Family Guy: "Cop and a Half-wit" (S15E15, OAD: March 12, 2017)
10:30pm-Family Guy: "Peter's Lost Youth" (S15E17, OAD: March 26, 2017)
11pm-The Daily Show
11:35pm-Family Guy: "A Bottle Episode" (S21E17, OAD: April 16, 2023)
12:02am-Family Guy: "Vat Man and Rob 'Em" (S21E18, OAD: April 23, 2023)
12:30am-Family Guy: "From Russia with Love" (S21E19, OAD: April 30, 2023)
1am-Family Guy: "Adult Education" (S21E20, OAD: May 7, 2023)
1:30am-South Park: "A Ladder to Heaven" (S6E12, OAD: November 6, 2002)
2am-South Park: "The Return of the Fellowship of the Ring to the Two Towers" (S6E13, OAD: November 13, 2002)
2:30am-South Park: "The Death Camp of Tolerance" (S6E14, OAD: November 20, 2002)
3am-South Park: "The Biggest Douche in the Universe" (S6E15, OAD: November 27, 2002)
3:30am-South Park: "My Future Self 'n' Me" (S6E16, OAD: December 4, 2002)
4am-South Park: "Krazy Kripples" (S7E2, OAD: March 26, 2003)
4:30am-South Park: "Toilet Paper" (S7E3, OAD: April 2, 2003)
5am-South Park: "Cancelled" (S7E1, OAD: March 19, 2003)
5:30am-South Park: "Fat Butt and Pancake Head" (S7E5, OAD: April 16, 2003)

Fun fact: one of comedy centrals predecessors (HA!) launched on April 1, 1990. The other one (the Comedy Channel) launched in the fall of 89.