“If it concerns an animal that may be brought as an offering to Yahweh, any such that may be given to Yahweh shall be holy. Another shall not be exchanged or substituted for it, either good for bad, or bad for good. If one animal is substituted for another, both that one and its substitute shall be holy. If it concerns any unclean animal that may not be brought as an offering to Yahweh, the animal shall be presented before the priest. The priest shall assess it, whether good or bad. According to the assessment of the priest, so it shall be. But if it is to be redeemed, one-fifth must be added to the assessment.”
You cannot switch the offering animals. However, if you want to take back your animal because of a blemish, it can be redeemed with a 20% fee added on. However, the assessment of the priest is the final word.