  Rare-earth nickelates RNiO$_2$ adopting an infinite-layer phase show
superconductivity once La, Pr or Nd are substituted by a divalent cation.
Either in the pristine or doped form, these materials are reported to adopt a
high symmetry, perfectly symmetric, P4/mmm tetragonal cell. Nevertheless, bulk
compounds are scarce, hindering a full understanding of the role of chemical
pressure or strain on lattice distortions that in turn could alter magnetic and
electronic properties of the 2D nickelates. Here, by performing a full analysis
of the prototypical YNiO$_2$ compound with first-principles simulations, we
identify that these materials are prone to exhibit O$_4$ group rotations whose
type and amplitude are governed by the usual R-to-Ni cation size mismatch. We
further show that these rotations can be easily tuned by external stimuli
modifying lattice parameters such as pressure or strain. Finally, we reveal
that H intercalation is favored for any infinite-layer nickelate member and
pushes the propensity of the compounds to exhibit octahedra rotations.
