Change Unity Tilemap's Tile sprite during runtime

ChangTiles.cs

using UnityEngine;
using UnityEngine.Tilemaps;

public class ChangeTiles : MonoBehaviour
{
    private Tilemap tilemap;

    void Start()
    {
        // @fixme
        tilemap = GameObject.FindWithTag("Tilemap").GetComponent<Tilemap>();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            SwitchTiles();
        }
    }

    void SwitchTiles()
    {
        BoundsInt bounds = tilemap.cellBounds;
        bool updated = false;

        foreach (Vector3Int pos in bounds.allPositionsWithin)
        {
            TileBase tile = tilemap.GetTile(pos);

            if (tile && tile is SwitchableTile)
            {
                if (!updated)
                {
                    Sprite sprite = ((SwitchableTile)tile).GetNextSprite();
                    ((SwitchableTile)tile).sprite = sprite;
                    updated = true;
                }
                tilemap.RefreshTile(pos);
            }
        }
    }
}

SwitchableTile.cs

using System;

#if UNITY_EDITOR
using UnityEditor;
#endif

namespace UnityEngine.Tilemaps
{
    [Serializable]
    [CreateAssetMenu(fileName = "New Switchable Tile", menuName = "Tiles/Switchable Tile")]
    public class SwitchableTile : Tile
    {
        public Sprite[] sprites;
        public Tile.ColliderType m_TileColliderType;

        private int spriteIndex = 0;

        public override void GetTileData(Vector3Int position, ITilemap tilemap, ref TileData tileData)
        {
            tileData.transform = Matrix4x4.identity;
            tileData.color = Color.white;
            if (sprites != null && sprites.Length > 0)
            {
                tileData.sprite = sprites[spriteIndex];
                tileData.colliderType = m_TileColliderType;
            }
        }

        public override void RefreshTile(Vector3Int position, ITilemap tilemap) 
        {
            tilemap.RefreshTile(position);
        }

        public Sprite GetNextSprite()
        {
            spriteIndex += 1;
            spriteIndex = spriteIndex % sprites.Length;
            return sprites[spriteIndex]; 
        }
    }

#if UNITY_EDITOR
    [CustomEditor(typeof(SwitchableTile))]
    public class SwitchableTileEditor : Editor
    {
        private SwitchableTile tile { get { return (target as SwitchableTile); } }

        public override void OnInspectorGUI()
        {
            EditorGUI.BeginChangeCheck();
            int count = EditorGUILayout.DelayedIntField("Number of Switchable Sprites", tile.sprites != null ? tile.sprites.Length : 0);
            if (count < 0)
                count = 0;

            if (tile.sprites == null || tile.sprites.Length != count)
            {
                Array.Resize<Sprite>(ref tile.sprites, count);
            }

            if (count == 0)
                return;

            EditorGUILayout.LabelField("Place sprites shown based on the order of switching.");
            EditorGUILayout.Space();

            for (int i = 0; i < count; i++)
            {
                tile.sprites[i] = (Sprite)EditorGUILayout.ObjectField("Sprite " + (i + 1), tile.sprites[i], typeof(Sprite), false, null);
            }

            tile.m_TileColliderType = (Tile.ColliderType)EditorGUILayout.EnumPopup("Collider Type", tile.m_TileColliderType);
            if (EditorGUI.EndChangeCheck())
                EditorUtility.SetDirty(tile);
        }
    }
#endif
}

@Sho2629 You need to create an asset as SwitchableTile, configure the sprites in order you desire - an asset is similar to prefab. Then apply your tile asset to Unity Tilemap.

The [SwitchableTile.cs](https://gist.github.com/KHN190/0d41c6a54a757d82f3a2814f5ff9d2a4#file-switchabletile-cs) needs to be placed in an Editor folder though. It is a Unity convention to organize your editor scripts.

You may want to search for keywords "Unity Tilemap", "Unity create asset" and "Unity editor script folder".

I don't understand "SwitchableTile always returns false" - it is an object / asset.