change the value of tag in xml column

I've got some code that adds new xml tag with the value of existing item to my XML MyColumn column in table MyTable.

UPDATE MyTable SET MyColumn.modify('insert element NewItem {/RootElement/ExistingItem/node()} after (/RootElement/ExistingItem)[1]')

What I want to do is edit this value presented as 开发者_JAVA百科xpath expression. Let's say I have value of "Test" in my ExistingItem element. And I want to have "something Test else" in my NewItem element.

What should I do?

---

Somewhat cumbersome solution, in case something simpler won't come up:

--sample data
declare @t table
(
    col xml
)

insert into @t select '<RootElement><ExistingItem>Test</ExistingItem></RootElement>'

--solution
--read existing element into a variable
declare @str varchar(50)
select @str = 'something ' + cast(t.c.query('data(.)') as varchar) + ' else'
from @t cross apply col.nodes('(/RootElement/ExistingItem)[1]') t(c)
--insert new element with the value of the variable
update @t set col.modify('insert element NewItem {sql:variable("@str")} after (/RootElement/ExistingItem)[1]')
select * from @t