The dust has not settled yet from the demotion of 36 teachers in the North Penn School District.   The school board took that action less than three weeks ago after the union rejected a six month pay freeze proposed as part of a package of cuts designed to balance the budget without a property tax increase.   Union President Alan Malachowski addressed the school board at its meeting on Tuesday night and asked that the demotions be rescinded.   District officials took no action on his request.   The school board did, however, ratify an agreement with district administrators from the superintendent on down that freezes their salaries for the rest of the calendar year.   District officials also say that the the support services union has a new offer on the table.   The budget approved by the school board last month calls for the layoff of 13 union members because an agreement on a pay freeze could not be reached but the renewal of negotiations could prevent the pink slips.