Can a wedding dress neckline be altered to make it more square?

I found my dress a few weeks ago and am really happy with it, but the only thing I would like to amend is the neckline. The neckline is a square shape, but with slightly rounded corners. I'd prefer it to be a bit sharper.

Would a seamstress be able to alter this?

The neckline in question is this:

But I'd prefer it if it looked a bit more like this:

Thanks!