Given application of enough force and/or mechanical advantage (aye, maybe even aided by lubrication or vibration?), I believe just about anything can be moved or de/re-formed. Someone/somewhere very long ago may have even made a statement something to the effect, "Give me a lever and a place to stand and I will move the world" (I would thus not underestimate the ability of some contractors to apply brute force, even inside a pipe!) It would appear however that most engineering and regulatory new construction specifications, getting into any degree of specificity with regard to installed/discovered over-deflection conditions (I have seen over the years and/or as I viewed in a brief web search), for whatever reasons now specifically require over-deflected pipes to be re-excavated, inspected, and/or relaid. I have not happened to see any such construction specifications that specifically describe or define other suitable/acceptable means/equipment for repair of such conditions.
It is nevertheless interesting (based on a similar brief web search) that apparently multiple entrepeneurs around the country are now somehow making a living out of such unfortunate happenings with over-deflected pipes (and most of these folks are also now specifically mentioning plastics). These enterprising folks are offering (I suspect for a price that is some below what it costs to dig them up) their various equipment etc. for re-rounding (I would think at least temporarily) same in the ground. What a country!
Other than knowing of this interesting state of affairs/apparent rather widespread conundrum with contemporary pipes/installations, I otherwise have no experience with such services.