GIF export including 4 specific color

Hello! I need to modify 340 static GIF files saved with 4 indexed colors. Each of the 4 colors should have a special HEX code. In Photoshop's export options, I can click on the swatches and change them manually. However, if I want to use the batch processing to change all files at once with a saved action, the wrong swatches are sometimes assigned the new colors, i.e. HEX values. Do you have a solution for this?