Adam Clarke on Romans 11:29

For the gifts and calling of God, etc. - The gifts which God has bestowed upon them, and the calling - the invitation, with which he has favored them he will never revoke. In reference to this point there is no change of mind in him; and therefore the possibility and certainty of their restoration to their original privileges, of being the people of God, of enjoying every spiritual blessing with the fullness of the Gentiles, may be both reasonably and safely inferred.

Repentance, when applied to God, signifies simply change of purpose relative to some declarations made subject to certain conditions. See this fully explained and illustrated by himself, Jer 18:7-9.