Hello fellow KB player
No it`s only for couple of fights. When you use some wanderer scroll like Titan sword (+10 attack), Titan armor (+10 defense) , Mana flow (+30mana), Mad rage (+30 rage), Depth of mind (+10intellect) , Ancient knowledge (+50% experience) little indicator will show in upper right corner of screen with number that show for how much battles that bonus last.
Other wanderer scrolls like Song of wind (flying units) , Call colossus (5th lvl units), Call of death (undead units) - give you some random units in your leadership amount. expl : if you have 1399 leadership and use Call colossus scroll you can only get 5th lvl unit with less then 1400lds/unit - Orge, Troll, Orc chieftain, BUT if you have 2500 lds and use same scroll you can get any 5th lvl unit since highest is Black dragon with 2500lds/unit, or you can get 2x(Troll/Ogre/Orc chieftain) or 1x(any dragon/Giant/Cyclop/...).Song of wind will give you random flying unit - pixies, griffins, highterran... Call of death obviously will give you any undead units in your lds amount, BUT not some you already have, so if you have just 1 skeleton archer in your army there is no way to get more of them with this scroll. If you want them place that skely archer in some castle and use scroll.
In the end if you dont like unit you get from some scroll, fight 1 battle and try again , OR use some item as : spider egg, thorn sprout ... but just 1 and then try scroll again. There is certain recipe on this forum to get 5th lvl units (like 1 sprout, 1 spider egg, 1 spider egg, 1 snake egg and then use call colossus scroll and get black dragon, for red dragon there is some other string of usable items). Good luck, have fun