I dont know if anyone has worked this out yet but I found out how to change soundtrack aswell as change the track inside the soundtrack. If noone has found this out yet tell me and I will post it.

what do you mean, just changing your custom sound track

that shouldn't be a puzzle, i think most of us know that already
just hold up or down for a second and it will change the track

if u hold left or rigth on the dpad u can browse songs that are on ur custom soudtrzck..idk about normal radios

yea i know what you mean it skips whole CDs and that sucks i never figured it out

Pause the game and in the audio settings change the cd mode from random to sequential. Now holding l/r the dpad will let you skip a single track or hold u/d to skip to the next cd.

I know its pretty much been answered but i have a Q in a different form,
How do you keep custom soundtrack on always or as default for any car?
Because lets face it, the songs on radio maybe ok but after awhile its just more commercial radio overplaying.