Quick thought, only one modification can be done with modify at the time, therefore it may be simpler to use either a query or FLWOR (For, Let, Where, Order by, Return) for multiple inserts.

😎

Here is a simple example of multiple modifications using query

DECLARE @OUTPUT XML;

DECLARE @X XML = '

<row id="1000000" xml:space="preserve">

<c1>Exported</c1>

<c2>Text Sample 1</c2>

<c2 m="2">Text Sample 2</c2>

<c2 m="3">Text Sample 3</c2>

<c2 m="4">Text Sample 4</c2>

<c3>Text Sample 1</c3>

<c3 m="2">Text Sample 2</c3>

<c3 m="3">Text Sample 3</c3>

<c4>Text Sample</c4>

<c5>Text Sample</c5>

<t1>Text Sample</t1>

</row>';

SELECT @OUTPUT = @X.query('

<row id="1000000" xml:space="preserve">

<ctest>Added before the first element</ctest>

{ /row/c1 }

<ctest>Added after c1 and before c2</ctest>

{ /row/c2 }

<ctest>Added after c2 and before c3</ctest>

{ /row/c3 }

<ctest>Added after c3 and before c4</ctest>

{ /row/c4 }

<ctest>Added after c4 and before t1</ctest>

{ /row/t1 }

<ctest>Added after the last element</ctest>

</row>

');

SELECT @OUTPUT;

Ouput

<row id="1000000" xml:space="preserve">

<ctest>Added before the first element</ctest>

<c1>Exported</c1>

<ctest>Added after c1 and before c2</ctest>

<c2>Text Sample 1</c2>

<c2 m="2">Text Sample 2</c2>

<c2 m="3">Text Sample 3</c2>

<c2 m="4">Text Sample 4</c2>

<ctest>Added after c2 and before c3</ctest>

<c3>Text Sample 1</c3>

<c3 m="2">Text Sample 2</c3>

<c3 m="3">Text Sample 3</c3>

<ctest>Added after c3 and before c4</ctest>

<c4>Text Sample</c4>

<ctest>Added after c4 and before t1</ctest>

<t1>Text Sample</t1>

<ctest>Added after the last element</ctest>

</row>