Question

Hello,
In a debate with Yaron Yadan you mentioned the Meiri, who says that all the negative attitude toward gentiles was only because of their bad behavior, but if in later generations their behavior became good, then one may even desecrate the Sabbath for them and relate to them as though they were a kosher Jew, so to speak…
Could I please get the source for this Meiri? It sounds really quite novel…
Thank you very much in advance.