To achieve frame-by-frame control over clothing in a Spine animation using Unity, you can use the Spine API to change attachments or skins programmatically. Here's a general approach:

1. Use Spine's Skin API: You can define different skins for each clothing item and switch between them at runtime. This is useful if you have predefined sets of clothing.

2. Control Attachments Directly: If you want to change specific attachments (like clothing) on a frame-by-frame basis, you can use the Skeleton.SetAttachment method. This allows you to specify which attachment should be visible for a given slot.

3. Integrate with Unity's Animator: If you are using Unity's Animator, you can create an integer parameter that corresponds to the frame or clothing index. In your script, you can update this parameter based on your logic (e.g., using Fungus) and then use it to control which attachment is shown.

Here's a simple example of how you might script this:

using Spine.Unity;

public class ClothController : MonoBehaviour {
    public SkeletonAnimation skeletonAnimation;
    public string slotName;
    public string[] attachmentNames; // Array of attachment names for each frame

    void Update() {
        int frameIndex = GetFrameIndex(); // Implement this to get the current frame index
        string attachmentName = attachmentNames[frameIndex];
        skeletonAnimation.Skeleton.SetAttachment(slotName, attachmentName);
    }

    int GetFrameIndex() {
        // Implement your logic to determine the current frame index
        // This could be based on an integer parameter from the Animator
        return 0; // Example: return the first frame
    }
}

In this script, attachmentNames is an array where each element corresponds to the name of the attachment you want to show for each frame. You would need to implement GetFrameIndex to return the correct index based on your logic, such as reading an integer parameter from the Animator.

rmx The example scene Spine Examples/Other Examples/SpineGauge.unity is a good example of how to play back a specific frame. Check out the script called SpineGauge.cs that is attached to the Skeleton GameObject named gauge:

However, as Spinebot has answered, the most common ways to change the appearance of a skeleton are to use skins or to replace attachments using the Skeleton.SetAttachment method. You can preview skins without playing back the scene, but if you want to change the appearance by playing back a specific frame of the animation, you must play the scene to preview it. (You can play the animation in the Inspector window while you select the skeleton data asset, but it can only be played in a loop, so it is hard to check the appearance at a specific frame.)
I am not familiar with the specifications of Fungus, so you may have no choice but to use that method, but I thought I would add this just in case.