It should be possible to select a segment from Excel cell location in Report Builder and therefore change the segment for multiple requests at once, the same way as you already can select the Report Suite or other values from an Excel cell.
This is an interesting concept. The only reason you can use select report suite from cell is because you can use the report suite ID to do so, since the friendly name of report suites and segments can easily change. Would you be interested in this feature if we were to require you specify the segment ID in a cell?