904 cable replacement '65

I know I am asking a lot of questions and I appreciate the patience of the forum members.

I did do a search and I have studied all the websites with pictures and instructions for the park cable.
1) Is it possible to replace the shift and park lock cable with the trans in the car. I think so - looking for confirmation.
2) I have read that it is not a good idea to remove the park mechanism housing by just unbolting it - is that true? Is something going to fly out and shoot across the garage or be damaged?
3) What is the right way to adjust the park cable at trans end? FSM says do it in neutral, another source says to do it in park.
Pretty sure these are original cables. Engine was rebuilt and trans was "supposedly rebuilt" (shifts great) but cables were not replaced. Park is inconsistent. I did adjust the park cable at the floor console shifter.