I am new to the Fire Emblem series and am a little confused by what I have read about seals. I am not nearly far enough into the game to have any seals or need to use them but I want to be prepared. It seems that seals are quite rare/expensive so I don't want to waste any. So my question is, when changing from tier 1 to 2 or between tiers will it cost a seal every single time? Or do classes become available to switch between for free once you have used a seal to access them once? For example if I move a level 20 tactician to grandmaster then to a tier 1 class, will it cost another master seal to become a grandmaster again?