1 - Open Kingdom Rush Alliance and create a new save file, then close the game;

2 - Ctrl + R to open the Windows prompt -> Then, type %appdata%;

3 - In the "kingdom_rush_alliance" folder, select the corresponding save file you created (Top slot -> 1, middle slot -> 2, bottom slot -> 3);

4 - Open it with any txt reader;

5 - Change the "difficulty" number to 4, do not change anything else in the document.

Why? Because this will remove redundancy from full-game runs, there's only waste of time in (re)beating the entire main campaign, with all the upgrades you acquired. Not only that, but this also avoids confusion and leads to a more challenging run than those on Veteran mode.