While I appreciate your bluntness in your response I would like to point out, respectfully of course, that you lack the authority to determine the future course of events and the dismissal of a suggestion.
I mean, putting aside the fact a member of HS that is involved with the development the server nebbed me telling you it's not happening, some things are just obvious, settled issues that were decided upon early in development. I don't really need a staff badge to tell you some things just won't happen.
It's going to be a no.
You will not be allowed to just yoink cars and put them in your garage. Period. At all. (until VIN scratching becomes a thing)
Sorry.
If Alex and Co. wanted you to be able to do this they wouldn't have bothered to implement PDM and the mechanics to purchase or rent vehicles. Why bother eventually implementing car boosting and VIN scratching mechanics? After all, why bother if you're just going to yoink local cars with no roleplay, little risk, no struggle and simply park them as if they're yours?
While I see the pure RP merit of "how does the parking attendant know?", that doesn't mean it's necessarily valid from a game development or balancing perspective. HS want you to interact with the rental/purchasing stuff. HS will want you to interact with the proper boosting mechanics when they come into play. HS doesn't just want you yoinking a upgraded Massacro off the streets with zero roleplay and parking it as if you own it. It is simply not meant to be done this way.