I would like to use "cheap oneway" to a different region but encountered some problems.

Suppose AAA is in region #1, MMM, NNN are both in region #2 and ZZZ is in region #3

Ideally I would like to book AAA-MMM-AAA-ZZZ (layover at MMM & AAA are both over 24 hours) but only be charged the miles for two fare component (AAA-MMM and MMM-ZZZ) rather than 3 fare components (AAA-MMM, MMM-AAA, AAA-ZZZ), which is much more expensive. When I try to book it online using multicity on the dates when all flights have availability, it errored out the second step when searching MMM-AAA

However, I can price out and ticket succesfully for AAA-MMM, NNN-AAA-ZZZ (AAA is stopover, not connection here) and is charged for only two fare components (region #1-region #2 + region #2-region #3). When searching NNN-AAA, only non-stop flights are shown even though there are choices with connection.

My question are:

1) Can I call to add MMM-NNN, making NNN a connecion and effectively travelling from MMM to AAA in the previous case?

2) If 1) is not possible, can I call to change NNN-AAA to another date with connection? The date of NNN-AAA I booked without connection is not ideal.

Thanks for your inputs.