i have multiple accounts and i went online with my testaccount, instaled updates and went back to my mainaccount.
result; i still can install hidden parts and none of my cars has been reset!!
to select your car and to avoid it will be reset, you have to do the same as with selfcreated stealth or chromelines.
i noticed that slammed cars are now even more glitchy.
*edit* i just went online and the cars i used got reset

i don't understand the logic of PD. the only thing i see are overpowerd cars. it's a damn shame they didn't something about it.