As far as I know, the terms of entry letter was never published, but it was widely reported in a U.S. trade publication. The terms of entry for Canada and Mexico were similar and in my view quite unprecedented.
Basically, as a condition of being admitted, Canada and Mexico agreed not to reopen any text that had already been agreed to by the then nine TPP members. At that time only three of the 26 chapters had been closed. But according to the U.S. trade representative this commitment extends not just to completed chapters but to any unbracketed or agreed text in all the rest of the chapters.
I am not familiar with any country ever agreeing to a condition like that in any trade agreement. It's a principle of trade agreements that nothing is agreed until everything is agreed.
Just to close, Japan was recently admitted to the talks, and there have been no reports of any such conditions being placed on it as a condition of entry.