Who can use this capability
Resourcing Administrators, Portfolio Editors, and Project Editors can edit custom fields and tags on a project.
Transfer time from one project to another
You can transfer historical time tracked from one project into another.
To transfer historical time tracked from one project to another, you can gather the total amount of hours for each person in the first project and create a new project. In the new project you will add each person with the total number of hours they worked in the old project and change the date in which they worked on the project to a date in the past.
Alternatively, you can tag projects with the same custom field or tag, so when you view the schedule or reports, you can filter to see data associated with all projects with that tag or custom field.
You cannot merge projects in Resource Management.