In my own experience over several decades, ticket reissues and fare repricing are two different things. Tickets need to be reissued for all sorts of reasons. In some cases (e.g., involuntary changes), the new ticket is an even exchange for the previous ticket. In other cases (e.g., voluntary changes), the new ticket must have the taxes and carrier-imposed fees recalculated, so there may be some add/collect or refund, but the base fare remains unchanged. Per the fare rules, if you change the first flight, or voluntarily change the route after flying the first flight, you pay $125 plus or minus any difference in taxes and carrier-imposed fees, but the base fare remains unchanged.