You write that your usual butcher "wasn't" available. Does that imply that the regular is now available? If so, take in a sample and ask him. We can suggest things to do, but, we can't see or smell the poorly cured meat. Poorly cured or preserved meats (or other foods like beans) can be iffy (even deadly). Remote advice would seem to be less safe than on site advice. If I suggest what to do and you get sick, that's on me. And I'm not that interested in you getting sick.
Creating sustainable life, beauty & food (with lots of kids and fun)
Bacon is cured by exposing it to sugar, salt and sometimes nitrites and spices. The nitrites reduce the amount of salt and time needed to cure the bacon and a thin slab can cure in a handful of days. After which, the bacon is smoked and then heated to an internal temp of 140F (-ish I think it needs to be over 138 for cured meats, but 140's a safe mark so that's what I do). So basically, bacon is cooked meat. I don't think it can be re-cured.
In the past, the goal of baconing meat was to help it keep at room temperature for months or years. This required a lot more salt than what we use now and quite often, the pork would have to be soaked in water to remove the salt prior to cooking. There were also kinds of bacon that didn't need cooking after curing. Being thin, it could hang to dry.
With modern day refrigeration, we now bacon meat more for flavour than for shelf life. Thus less salt and more cooking.
What concerns you most about your bacon? The look? Flavour?
If it's flavour and you aren't happy with it. That's as good a reason as any to take it back.
As to changing the cure on finished bacon - that would be tricky. Perhaps finding recipes to use it in that cook it really well would be a good use for the bacon? Fry it then put it in soups?
It would be easier to make your own (which is super-easy). make your own bacon at home.