Copy activities between projects while retaining activity ID

I have a high level schedule and a detailed schedule. I want to copy the activities from the high level schedule to the detailed schedule so I can check an monitor if the detailed schedule keeps within the boundaries of the high level schedule. For this I need to keep the activity id's the same when copying so I can keep comparing also with the high level schedule.

What I tried was to open the high level and detailed schedule in a program and then copy and paste the activities, but when I do it like that the activity id's change.