No, there isn't really. You can remove the constraints by commenting out
tk2dSpriteCollectionEditorTextureView.cs, line 489 (or so)
param.anchorX = Mathf.Clamp(Mathf.Round(anchor.x), 0.0f, texture.width);
param.anchorY = Mathf.Clamp(Mathf.Round(anchor.y), 0.0f, texture.height);