Campaign editor.

You download the game file editor from here: /topic/1181/. Unzip it and open ResEdit2, then find the data folder. Next, the original Campaigns are located in heroes4.h4r - game_maps - campaign, The Coming of Arthas campaigns are in storm.h4r - game_maps - storm_campaign, and the Armageddon's Blade campaigns are in x2.h4r - game_maps - wow_campaign. Choose the desired Campaign, extract it, make the necessary changes using the map editor, and repack it.