At least, these are in the Commentaries, that is, in Visuddhimagga. But forcing breath is not there.counting breaths, which, while not directly spelled out in the suttas, has been used in anapanasati for centuries. The use of "Buddho" is not spelled out in the suttas either, but it still counts as anapanasati. Another example is the visualization of nimittas at the nose tip and so on.
These developments are not directly in the suttas but they are all still anapanasati.
Traditional theravadin commentarial interpretation. Here, a remark by Ven. Bodhi to MN 118:“Ānāpānasati method”? Whose interpretation? I see nothing in the MN 118 that says anything about the rate of one’s breathing.
The practice of mindfulness of breathing (anapanasati)
involves no deliberate attempt to regulate the breath, as
in hatha yoga, but a sustained effort to fix awareness on
the breath as it moves in and out in its natural rhythm.
Mindfulness is set up at the nostrils or the upper lip,
wherever the impact of the breath is felt most distinctly;
the length of the breath is noted but not consciously controlled.
The complete development of this meditation
method is expounded in MN 118. For a collection of texts
on this subject, see Bhikkhu Ñyanamoli, Mindfulness of
Breathing. See too Vsm VIII, 145–244.
Forceful breath not only isn't there, but it contradicts traditional understanding. But, of course, it is up to you whether to follow something or not, practise or not.As for what is not found in the suttas and commentaries, one can find in the teachings of Ven Thanissaro, for example, a lot of differing things to aid one’s practice that are not found in the suttas or commentaries, but they work in helping the student learn, see, gain confidence – saddhā – etc.