SHELL

sed replace in file

sed -i 's/foo/bar/g' hello.txt

replace using sed

#on my mac
sed -i -e 's/old-text/new-text/g' text.txt

sed replace

For using match in sed replacement, just border it with '(' and ')':
echo Before123 | sed 's/Before([0-9]*)/1After/g'
123After	# number is matched withtin '( )' and replaced in '1'
Example with 2 match replacements
echo a_b | sed 's/(^.*)_(.*$)/first is 1 and 2 is after/g'

sed replace into new file

You can try this sed command

sed 's/,(.*china)/,Tomas_proxy.lt/1/' FileName
or

sed 's/,(.*china)/,Tomas_proxy.lt/1/' FileName > NewFile
or

sed  -i.bak 's/,(.*china)/,Tomas_proxy.lt/1/' FileName