string - Mask data in a specific postion and specific record type -

updated:

i have file quite big. need mask characters in specific postions , specific record type. have searched on place cannot find solution of quite simple task. here example

file name: hello.txt

file:

0120140206input file
1032682842 mr simpson
20231458 742 evergreen terrace
3034560817 green
1032682842 mr griffin
20231458 spooner street
3034560817 red
3001

what mask position 12-16 of lines starting 10. this:

0120140206input file
1032682842 xxxxxmpson
20231458 742 evergreen terrace
3034560817 green
1032682842 xxxxxiffin
20231458 spooner street
3034560817 red
3001

try this:

sed 's/^\(10[0-9]\+[ \t]\+\).*$/\1xxxxxxxxxxxxx/g' 

example:

sed 's/^\(10[0-9]\+[ \t]\+\).*$/\1xxxxxxxxxxxxx/g' <<< "0120140206input file 1032682842 mr simpson 20231458 742 evergreen terrace 9001"