Aruch Hashulchan (603) says:
…so he wrote that even someone who is not careful all year with bread of a non-Jew should be careful during the ten days of return, q.v.
It seems to me that that's true only of things that have no legal prohibition — like this, which is only a pretty thing to do (hidur), so it's appropriate to prettify thusly during these days. But things that some people have ruled are prohibited legally, but that people act on according to the lenient ones, such as chadash outside Israel, flesh without an adhesion, and the like — one cannot act thusly [=in accordance with those who rule stringently] during the ten days of return. After all, since [those who might do so] would be refraining from eating [such food] during these days, it'd be as if they accepted the prohibitors' view upon themselves, so how could they eat it afterward?
It seems that Aruch Hashulchan holds that the "it'd be as if they accepted the prohibitors' view upon themselves, so how could they eat it afterward?" argument does not apply to pas palter, bread of a non-Jew, and that he'd thus not require hataras n'darim, which would be specifically for something that, without such hatara, would remain prohibited.
If I might add my own thoughts — hataras n'darim requires that the person seeking the hatara have a pesach, some situation that has arisen that he did not anticipate when making his neder: had he anticipated it, he'd never have made the neder. If that were required here, then presumably "it's too hard to keep this rule all year" is insufficient a pesach year after year after year: at some point, he should anticipate it's not going to work. So he'd need some other pesach. Yet we find no mention in halacha of hataras n'darim or finding a pesach or specifying "b'li neder" about pas palter in the ten days of return. That alone seems strong evidence that it's not considered a neder affecting the time after Yom Kipur.