In your current project, you can easily create your new activities; make sure to add good information such as: WBS, Activity type, activity ID, duration, resource type, Relationships, activity codes, and more,
Once everything is set in the project.
You can now open the project and the project baseline at the same time.
You can put a filter to work only on activities newly created.
Copy these activities in the Baseline Project (be sure to have in the baseline the good WBS) and especially the good activity ID (same as in the project).
Once activities are copied, open only the project baseline and do the reschedule with data date = project start date.
You can also do the reschedule to the project, with the current data date.
Re-assign the baseline to the project and verify important dates, and budget also.
I hope this will help.