Yes. In the first case, after uploading the new pics you might need to go to a picture already in the project and scroll down an add the pictures to the project from there. In the case of combining two projects, you might have to remove all the photos from one of the projects first (scroll down and double-click them to remove them from the project). You can change the order of pictures within a project by just clicking and dragging within that box of project pictures.
Remember that when adding pictures to a project, there's a search bar that will at least search the titles you've given each image, which I found helpful when going back to combine 26 images into a single project.