Hey @sh030901 !
I hope everything is going well!
It’s possible to modify the asset, and you can 3D editor to create rigs, animations, and so on.
Just keep in mind that you should carefully read the license for each asset, as not all of them are the same, some only allow personal, non-commercial use. You also cannot modify the assets for resale.
In case you’d like to read it, here’s the Fab End User License Agreement
I hope I have been able to help! 