yup thats right. with the hob filters,you want to only change one part at a time else risk messing up your cycle. for the internal ones like morado has,well what i do is put an extra filter catridge in fishys tank. that way,there is always an extra cycled.
if you dont have another cycled tank,keep the extra filter or a sponge for a filter in that tank you have,so its ready to go pretty much. just would suck if you have a small tank,cause that would take up extra room.
wow i feel kinda smart,even though i havent had fish for very long haha...