Can you alter a sweetheart to square neckline?

That’s something only they can answer. Browse Yelp in your area and read reviews there because unlike TheKnot which are removed at the vendor’s whim, the ones at Yelp cannot be removed at their request. Don’t hire the first seamstress you talk to either.

I feel like if you found a good seamstress and ordered more fabric from where you bought your dress, it would be possible. Definitely do your research on local seamstresses and figured that out