Not necessarily. The true is that you can not paste whole row at once as a new row in another project. But it is possible to copy and paste e.g. structures and other columns which have allowed modifications in the new project(not those one I've mentioned in the last post).
In order to copy several structures, select them in source project, create new (empty) rows in target project and select an area of structure column of the same size as in source project. See attached images.
This can be useful for copying several structures, but transfer of all data can not be guaranteed(not all columns has to be shown).
For copying bigger amount of whole rows you can flag each row you want to copy(e.g. by adding new discrete text field) and search those at ones. Export and import are simple procedures at the end of migration process between projects.
Hope it helps!