If the others want to follow their lead, they will have the liberty to do so but will not be compelled to implement any changes they don't feel applies to them. The P5 will be able to craft or amend legislation without having to get approval from the majority of D1's 351 members.
Think of it as a big conference. The ACC can implement internal rules/regulations that apply only to them and not, for example, the Sun Belt.
To answer your question, no we are not in the P5. TH said that BYU will stay with the P5 when the move occured and that means that BYU will adopt any legislation the P5 implement so that the gap doesn't become wider.