I guess AWK should do it. If the fields are fixed then just print them.
Something like this

echo "<log4j:event.........schema="LMS">" | awk '{ print $3,$4, substr($5,3,5), $5...'}
Here $3, $4 prints te whole word/field and substr($5,3,5) prints 5 characters of 5th field starting from the 3rd letter.

Modify the awk with your requirements.

Thanks and Regards,
Gideon.