I would probably take it a step further, to avoid repeatedly indexing into the array:
var
Idx: integer;
Rec: ^TSomeRec;
// [...]
Idx := CountInMyArr;
SetLength(MyArr, Idx + SomeDelta);
Rec := @MyArr[Idx];
Rec.SomeField := SomeValue;
// and repeated for each field in TSomeRec
Inc(CountInMyArr);