In Pathfinder, does a one-attack monster lose its x1.5 strength bonus when gaining an additional attack type?
This question came about when beastshaping into a one-attack animal but temporarily granting it an additional weapon through the Transmuter (Shapechanger)’s Battleshaping ability, which simply allows you to grow an additional natural weapon.
The rules on natural attacks state:
Primary attacks are made using the creature’s full base attack bonus and add the creature’s full strength bonus on damage. Secondary attacks … add only ½ the strength bonus on damage rolls. [...] If a creature has only one natural attack, it is always made using the creature’s full base attack bonus and adds 1 + ½ times the creature’s strength bonus on damage rolls. This increase does not apply if the creature has multiple attacks but only takes one.
There are some monster entries which specifically state that a weapon gains x1.5 strength regardless of situation, but let's ignore those for this question.
Does a One-Punch monster lose its strength advantage when gaining an additional attack?