Can I copy selected activities from a project/template to a project in OPC?

I need to copy selected activities from an OPC template (or project) to a project. I have a convoluted way of accomplishing my goals via importing from Excel, but it's cumbersome. Am I missing something obvious? I know I can't have multiple projects open except through a program, but that doesn't allow me to copy/paste activities. I've seen discussions about copying a WBS, but I haven't discovered how to do that or if it's what I want. I do not want the activity IDs renumbered unless there is a conflict with the existing activities.

Thanks for any ideas,

Christine Monks