You can add another email to a sequence which is already sent.

Scenario 1

Many leads maybe mid-way somewhere in the sequence, who haven’t reached the ‘processed’ state yet, who haven’t got to the last email yet, all those will automatically get the last newly added email in the sequence.

Scenario 2

There will be many leads who are in ‘processed state’. For whom, the sequence was already over. You can filter all these leads who are in ‘processed state’ AND who were ON THAT sequence, and click on ‘Continue Followup’. Then those leads will get the last newly added email as well.

Make sure you do not select leads who have already responded positively or negatively - otherwise they will not like it that you are sending more emails to them even when they have responded to you. For this you can use the state filter and filter on Cold and Warm leads only.