What to do with over cooked quince jam
You might consider making your own membrillo.


  Quince cheese, also known as dulce de membrillo, is a sweet, thick, jelly made of the pulp of the quince fruit. Quince cheese is a common confection in several countries, where it goes by various names, such as [. . .]


It's a really great option and pairs beautifully with cheese and crackers. I've never made it before but there are some guides on the web and, considering it's essentially a very dense jelly, it may be ok with your dense quince fruits.