Recently had a small stress crack on my p3a, and since my warranty will be out in December thought to send it in.
Received the drone back.
New shell everything is cool.
My question is

I kinda feel that new shell is a bit different then the old one. Not visually but material by touch feels different.
So they replace shells and install a newer better versions of them? Or its just seems so cause its new?

They did re-design the shell at one point to help strengthen the motor mounts. There are a number of older posts on the forum about this.

Get a torch. Shine under the motors. If you an X pattern brace then that's the reinforced shell.
Another is to look at the vents. The latest shell has bigger air vents.
Another is to remove the motors and have a look at the 4 motor tabs. The new reinforced arms have notches in the motor mount tabs.

And also, if you want to prevent cracking, lower the active braking to 70-80. This means the Phantom behave a little like a P2 and wont stop on a dime if the sticks are let go. I do believe the sudden braking causes stress on the plastics.

Yes, DJI made minor changes to the moulds but no, they make no difference to cracking or not cracking (just like changing active braking settings).
Whether your shell develops cracks (and most never have) depends on the quality of the plastic used in the moulding.