Is being made a full heir the same as being born again?
No, they are not the same. At salvation a person is born into the family of God by the Holy Spirit, but God performs another act that places him as a full heir with Jesus Christ. Being a full heir is an additional placement, not merely the new birth, and it is granted the moment one believes.
Les explains that the term means we are placed as a full son, not just as one born into the family, nor as one legally taken from another family. He notes that at salvation we are born into God's family by the work of the Holy Spirit, but immediately God also places us as the full heir with Jesus Christ. This is another act of God, not something we strive or strain to attain. As joint heirs, we share equality with Christ—what is His is ours.