return a custom image based on the name of the requested image within a bundle. this should only be used when filtering a specific app in your bundle filter plist

OverrideImageInBundle.m

%hook UIImage

// you should not include the file extention or scale in the file name for this to work
// I have not tested this, but it should work for any image being loaded from the bundle
// baseNameOfLaunchscreenImage@2x.png -> baseNameOfLaunchscreenImage

+ (UIImage *)imageNamed: (NSString *)name {
    if ([name containsString:@"baseNameOfLaunchscreenImage"]) {
        return [UIImage imageWithContentsOfFile:@"/User/Documents/CustomLaunchImage.png"];
    }
    return %orig;
}

+ (UIImage *)imageNamed:(NSString *)name inBundle:(NSBundle *)bundle compatibleWithTraitCollection:(UITraitCollection *)traitCollection {
    if ([name containsString:@"baseNameOfLaunchscreenImage"]) {
        return [UIImage imageWithContentsOfFile:@"/User/Documents/CustomLaunchImage.png"];
    }
    return %orig;
}

%end