I'm currently gold. I have two round trips coming up this month, and the MQMs from these two trips together will push me to platinum when I get done with both of them (and I have AmEx waiver). With a bit of creativity, I can get to platinum after the first trip and have the status for the second trip. However, since I've never done SDC before I'd like some advice.

Next Saturday I'm booked in economy V class with routing MSN-MSP-EWR, and a corresponding return trip a few days later. I'm not sure how to find official routing rules, but I can say when I booked this, there were no 2-stop itineraries available in that fare bucket. I have a pretty reasonable FCM upgrade offer and assume that I get 150% MQM if I do it, but even then I don't hit platinum this time. However, if I could change my outbound to MSN-MSP-ATL-EWR, that would do it. I could purchase the proposed routing on delta.dumb right now (classes are A and/or F). It's a Saturday afternoon flight and the F and C+ cabins are virtually empty, so I think I'd have a reasonable shot of at least one open seat in first at T-24, although I realize this is not guaranteed.

Questions:
1. If I do the FCM, would the MSN-MSP-ATL-EWR routing then become accessible/valid for me (assuming requisite seat availability)?
2. Can the SDC be performed online or does it require an agent?
3. What are the chances an agent looks at this and says, "your proposed change involves more flights and it takes you longer to get there -- that doesn't make sense so I'm not changing you."