While it isn’t possible to merge projects in 10,000ft, if you want to transfer historical time tracked from one project into another, each person could bulk enter their historical hours for the old project into the new project and specify a date in the past (i.e. August 1, 2017) when everyone should enter their historical hours to the new project.
Alternatively, you can tag projects with the same convention, so when you view the Schedule or Reports, you can filter by that project tag to see data associated with all projects with that tag.