Does the significance (importance) assigned to food within Judaism change in particular environments or on special occasions?
Yes. The matzah, or unleavened bread, is to remind the Jewish of the times when they had to flee from Egypt and so it is significant on certain occasions only.
Jewish holidays like Passover or Hannukah both have traditional foods that have a particular sigificance for that holiday. For example, potato cakes and a certain type of doughnut are popular on Hannukah because they are cooked in oil, which reminds people of the miracle of oil burning for eight days straight. During Passover, Matzah is a staple food because the Jews only had unleavened bread on their way out of Egypt. On these special occasions, foods take on a particular importance that they don't have during the rest of the year. There are special dietary laws just for these occasions. During the rest of the year, the Jewish dietary laws remain consistent, assuming of course a person chooses to adhere to these dietary laws, which not all Jews do.