The cheats were made by myself and will only work on the American version of the game.
Emulator: https://github.com/notaz/pcsx_rearmed
Recording tool: FFmpeg
Comments: https://photos.app.goo.gl/L4y5Lo4xgd4qCDZV8

Cheats' memory addresses and values:
Drive through cars/objects: 8011DC94 7FFF
Player car (R2; can be used to apply other paint jobs):
E012E2F3 00FD
300F9FEC 00XX
Traffic amount: 300F9F5C 0003
AI cars (SELECT; may cause graphic glitches):
E012E2F2 00FE
300FA090 00XX (1st AI/opponent)
E012E2F2 00FE
300FA134 00XX (2nd AI/opponent)
E012E2F2 00FE
300FA1D8 00XX (3rd AI/opponent)
E012E2F2 00FE
300FA27C 00XX (4th AI/opponent)
E012E2F2 00FE
300FA320 00XX (5th AI/opponent)
E012E2F2 00FE
300FA3C4 00XX (6th AI/opponent)
E012E2F2 00FE
300FA468 00XX (7th AI/opponent)
Have ABS brakes: 300FA03C 0001
Driving aids:
300F9F6C 0000 (Ghost car [hides player car in races])
300F9F78 0001 (Tutor)
300FA038 0001 (Traction)
300FA040 0000 (Braking)
300FA044 0001 (Best line)

00XX = 0000 (Ferrari 355 F1)
00XX = 0001 (Chevrolet Corvette)
00XX = 0002 (Lamborghini Countach)
00XX = 0003 (Italdesign Nazca C2)
00XX = 0004 (Ferrari 550 Maranello)
00XX = 0005 (Lamborghini Diablo SV)
00XX = 0006 (Jaguar XJR-15)
00XX = 0007 (Mercedes Benz CLK-GTR)
00XX = 0008 (El Niño)
00XX = 0010 (Pursuit Chevrolet Corvette)
00XX = 0011 (Pursuit Lamborghini Diablo SV)
00XX = 0009-0026 (Any value between 0009 and 0026 will set a traffic or cop car.)

Cheat hotkeys (refer to https://www.cheatcc.com/psx/codes/jokercom.html#mainContent):
E012E2F2 00??
E012E2F3 00??
D012E2F2 ????
D = 16-bit addressing; E = 8-bit addressing.