Change of name after WWI in Poland? #names

Roberta Schoen

My grandfather arrived in NY in Aug 1912 alone from Jedwabne and left his wife and 3 children in Poland, with the intent to send for them when he’d made enough money.  His name was Abram Kulawski in the ships register and in the list of inhabitants in Jedwabne before 1939.     WWI broke out before he could send for them but they reunited after the war.  She and the 3 children came to NY in Aug 1921, but the last name is listed as Kulaska.   I have a paper for my aunt that reads in Cyrillic letters KALASKA.    
I know that Jedwabne was on the border between Poland and Russia during WWI.   I’m not sure who controlled Jedwabne between the wars.    Would people have changed their last names to more Russianized versions after the war?  Would that be voluntary or imposed by the government?   Or would there be a different reason for the name change?
                  Roberta Schoen
Researching KULAWSKI in Jedwabne, Poland;  EMIL in Stawisk/Stavisk/Stawiski, Poland;    RAPPAPORT in Odessa;  SCHATZ in Goldingen, Latvia;   LIPSCHITZ in Kuldige/Ventspils, Latvia

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