I did some quick research on this, well I checked some Wikipedia articles which is the most research this topic deserves, and I found out that the Nobel Peace Prize is usually decided in September and announced in December. Apparently sometimes the decision is made in October. The Munich agreement was made on September 30th, 1938, and Germany invaded Poland on September 1st, 1939.
Hitler was not awarded the Nobel Peace prize for the Munich agreement because he reneged on the agreement too quickly and the agreement came too late in the year. But suppose the Nobel people were taking a long time to decide in 1938, so they could still award it right after the agreement was announced, and awarded the prize to Hitler and Chamberlain.
Would this have any effects worth mentioning at all?
Gandhi was never awarded a Nobel Peace Prize.