Here is a mod I wanted long time, HD mod has it but I have problems with HD mod, so now will work in era. Still I am not able (or too lazy) to calculate the exact percentage of experience when reunite multiple stacks (for now stack clicked experience is shared), so if anyone wants to brag about and improve, be my guest.

Army Management

Hold Shift + right-click on stack to divide that stack in equal parts
Hold Control + right-click to divide that stack in 1 creature stacks
Hold Alt + LEFT-click to unite all creatures of same ID in one stack

Note: Only a max of 4 warlord banners can be stacked on one stack, therefore when you unite mutiple stacks having multiple banners, all banners except one will be given to hero backpack.