Western Ukraine and western in Belarus were not in alliance with Poland. In alliance were Polish minorities living in western Ukraine and western Belarus. Poland engaged in a war that we’d call a hybrid war in modern times. Common folks and middle class of western Ukraine and western Belarus wanted to join Ukrainian and Belarusian republics believing they would have their own states enjoying their languages and cultures in schools and cultural centres. Western Ukrainians were russophiles from late 19th till 1939 greeting Soviet arrival with flowers. https://en.wikipedia.org/wiki/Western_Ukrainian_Russophiles
Not until west Ukrainians and west Belarusians met the Russians who sent them NKVD responsible for execution and deportations of thousands who were deemed to be not trustworthy to Soviet government Also there were xenophobia and chuavinism towards Ukrainians and Belarusians. Hence a fall-out with the Russians. Polish cultural opression were even worse. I can find you figures on the number of schools, universities, media, cultural centres were close. Most than 90% were closed according to Ukrainian and Polish sources. Many Orthodox Churches in Volyn and western Belarus were also closed by Polish authorities.
Stop spreading Polish propaganda about retrieving Polish land before partion of Polish-Lithuanian Commonwealth. Present day Belarus and Lithuania were part of Lithuania that had its separate constitution, courts, administration, border customs that was in confederation with Poland since 1569. Poland and Lithuania were two separate states forming a confederation.
I am not implying Poland should be keeping commie toponyms. I hope all those are removed with some exceptions to those people or organisations who significantly contributed to the developement of towns or districts. There are such instances.