Depends on what you mean. If you mean add the information to the projectile database, I don't believe you can.
If you mean setup a screen with your data for your projectile with the appropriate ballistic information to review, yes. Just save it as a "User File". You can recall it at any time after that.
Setup the information on the screen with the projectile name, weight, BC and the rest of the information.
Select User Files on the bottom of the screen
where it says, DATASET, change it to whatever you want to call the file
Done.
To recall, choose UserFile on the bottom of the screen, touch the file you want and it comes back