This is the similarity between the Altar and the Temple consecrations: both cannot be changed to another type of sanctity. If the owner of an animal that has been consecrated to the Temple for its value decided to change its sanctity and consecrated it to the Altar, he has accomplished nothing. Although Altar sanctity is higher than the Temple sanctity, it still does not take effect.
In the same vein, if an animal has already been consecrated to the Altar as one sort of offering, for example, as a peace offering, its sanctity cannot be changed to another one, such as burned offering.
If an animal consecrated for the Altar died, it must be buried. It cannot be redeemed, because, since it died of itself, even after redemption it can be only given to the dogs to eat, and it is not fitting to redeem a sacrifice if all we can do with it is feed it to the dogs. Some say that the reason here is different: even if the animal died through proper kosher slaughter, for redemption it has to stand up, as the Torah said, “and he shall stand the animal... and evaluate it,” and a dead animal cannot stand up.
Art: Laszlo Mednyanszky - Burial in the Carpathian Mountains