Я бы сделал это
sed -r '
# for lines without "ASSERT.", add a newline before "SP."
# unless it is only preceded by whitespace
/ASSERT\./! s/^(.*[^[:blank:]].*)(SP\.)/\1\n\2/
# for lines containing "ASSERT.", add a newline before the last "SP."
s/^(.*ASSERT\..*SP\..*)(SP\..*)/\1\n\2/
' file