Low receptivity and ignored (rejected) are two different things. I think that if there is low or no receptivity, and if there is no alternative protein source, I imagine the ants would take the food.
Most of my colonies rejected wax worms initially, but, I did not provide another protein source. Now, most take the wax worms. Some of those Colonies are growing, and others are not. Some look like they are ready for hibernation. I only know that they take a food source that they initially rejected when no other source was offered.
I think that you are right that fresh unaltered protein sources are preferred though.