CJ,
Assuming your users are all at Seq 1 Delay 0 they will be queued to receive the first and then other followups you add. The same is true when users are at the end of the followup sequence and you add a new followup.
When adding a followup you can use the option "Reset all users on this Seq # to new delay" to ensure a specific delay for users on that Seq # before the new followup is sent.
Currently the only way to avoid sending existing users new followups is with a custom MySQL query with a program like PhpMyAdmin. To queue list 1 users for followup 3 with a delay of 48 hours (or, more accurate, skip 1 dailymail...) use a seq of 3 and delay of 1.
UPDATE lm_users SET cseq = '3', cdel = '1' WHERE list = '1';
Regards