(a) yes, the impact of removeing all the organisms in a trophic level will be different for different trophic levels. For example, in the food chain : Grass`to` Deer`to` Lion :
(i) If we remove all the lions at the third trophic level, then the number of deer will increase too much . All these deer will eat up all the grass and other plants turning the forest into a desert.
(ii) If we remove all the deer at the second trophic level, then lions will not get sufficient food, they will starve and die. Deer eat grass and other green plants, so the amount of grass and other green plants will increase too much.
(b) No, all the organisms of any trophic level connot be removed wihout causing any damage to the ecosystem.