How to set IsModified to false on a property in a related Collection in EF Core?

I am using Asp.Net Core 1.1 and I have two classes:

public class Scale
{
    [Key]
    public int ScaleId { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }

    public decimal DefaultValue { get; set; }

    public List<ScaleLabel> Labels { get; set; }
}

public class ScaleLabel
{
    [Key]
    public int ScaleLabelId { get; set; }

    public int ScaleId { get; set; }
    public virtual Scale Scale { get; set; }

    public decimal Value { get; set; }

    public string Label { get; set; }
}

When a scale is used, all its ScaleLabels should be prohibited to update except for their Label property.

    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Edit(int id, [Bind("ScaleId,Name,Description,DefaultValue,Labels")] Scale scale)
    {
        if (id != scale.ScaleId)
        {
            return NotFound();
        }

        if (ModelState.IsValid)
        {
            try
            {
                if (IsScaleUsed(id))
                {
                    _context.Scales.Attach(scale);
                    _context.Entry(scale).Collection(c => c.Labels).IsModified = false;
                }
                else
                {
                    _context.Update(scale);
                }
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ScaleExists(scale.ScaleId))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }
            return RedirectToAction("Index");
        }
        return View(scale);
    }

If I use _context.Entry(scale).Collection(c => c.Labels).IsModified = false; then nothing is updated, and if I don't use it, then all ScaleLabels are updated. I want to specify which properties of the Scale's Labels navigation property are modified and which are not.