Rom 2: 28-29 A person is not a Jew who is one only outwardly, nor is circumcision merely outward and physical. No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit
Rom 9: 6-8 For not all who are descended from Israel are Israel. Nor because they are his descendants are they all Abraham's children. On the contrary, "It is through Isaac that your offspring will be reckoned." In other words, it is not the natural children who are God's children, but it is the children of the promise who are regarded as Abraham's offspring.
But to use those texts as support for their theology, the replacement promoters need to totally ignore the clear context of their proof texts.
Regarding Romans 2:28.
Go back several verses and you will read in verse 17:
“ Now you, if you call yourself a Jew; if you rely on the law and boast in God…”
It is specifically addressed to Jews who were trusting in their blood heritage and their relationship to the law. Paul was saying their heritage was not enough. It was not addressing gentiles and saying they have been made Jews through "circumcision of the heart". It was addressing Jews, saying that MORE than heredity and law observance were needed to be part of God’s people. An inward change worked by the Spirit is necessary.
Regarding Romans 9.
When Paul writes “not all who are descended from Israel are Israel.” He is referring to a faithful remnant of the descendants of Abraham Isaac and Jacob.
The statement is excluding SOME of those descended from Israel - it is NOT a statement intended to include others who are not descended from Israel.
It is not a statement that redefines what Israel means. It is a statement that refines what Israel means.
It does not shift the identity of Israel from one group to another - it narrows down the identity of Israel from a wider inclusive ethnic group to a smaller specific section of that wider group.
It pinpoints the faithful remnant AMONG the descendants of Abraham, Isaac and Jacob. It is not transferring attention outside of those descendants.
It's like saying that not all born into a Christian family are Christian - only those who have their own faith in Jesus.