@flowtoolz - OCP is def a solid principle (pun intended) to respect. Across modules (not within module building) it applies almost definitively. Though, within your own module being built, this usage (i.e., ‘selfprivate’) is not technically breaking that principle’s intentions, since you are not looking to modify implementation. Rather, you want to increase or maintain accessibility safety; which may also prevent file bloating, etc. I’d argue this can improve maintaining original implementations when thought for future changes (which supports SOLID).
An important clarification [presumed], is that the ‘selfprivate’ is NOT intended to allow accessibility outside of a module even if (e.g.) ‘class’ is set as ‘public’, since that is already available via ‘open’ and ‘public’.
Anyhow, a “+0” isn't negative 
- thanks