Quick answer: not likely. I opened one of my OmniOutliner documents where knew I had pop-up lists. I selected three rows and then tried different modifier key combinations while clicking on a pop-up list. None of the possible combinations of the ⌘ (command), ⌥ (option), ⌃ (control), and shift keys facilitated choosing a pop-up list item and applying it to all selected rows.
What you are asking for is similar to what can be done in Microsoft Excel; and is also sadly absent from Numbers. For those unaware, in Excel you can select a range of cells, enter a value in the focus cell, and then press ctrl + enter to have that value placed into all cells in the selected range. Similar functionality would definitely be a nice addition to OmniOutliner.