#!/bin/bash
s='Line title "A" - TOKEN some line with "quotation marks"'
sed -E ':A; s/(TOKEN[^"]*)"/\1/g; tA' <<< "$s"
# => Line title "A" - TOKEN some line with quotation marks
sed -E ':A; s/(TOKEN[^\\"]*(\\.[^\\"]*)*)"/\1\\"/g; tA' <<< "$s"
# => Line title "A" - TOKEN some line with \"quotation marks\"