The "pre-carbonized" on pipes I've seen is just a coating. If you try the old "wet finger" or "honey finger" method on a new pipe, the coating comes off on your finger!
I've tried the 5 Brothers to break in, using the "1/3 full for a dozen smokes" followed by "half full", "3/4 full" etc. I used 5 Brothers because it burns so fast and I could break in the pipe faster with several burns a day. I thought. After a week and about 2 dozen varied loads, I could detect NO cake build up. So much for 5 Brothers for break in.
My newest pipe is a Tinsky PSF POY and I asked Mark how I should break it in (it was coated). He said to fill it up and smoke it, and that's what I did. No partial bowl nonsense. It started caking very well using 4noggins Down By the River burley. (Burley builds cake fastest, I've heard.)
When breaking in a new pipe, whenever I taste burning wood (yuck!) I STOP smoking immediately. I let it cool off, tamp and relight, smoking slowly. After several smokes the wood burning decreases and then stops and I declare the pipe broken in. You should never taste burning wood on a broken-in pipe.