Torah Temimah cites Zevachim 9b.
“And he shall slaughter it as a chatas” — for the sake of that particular chatas; but if he slaughtered a chatas of forbidden fat for the sake of a chatas of blood, or for the sake of a different chatas, it is invalid.
Diyuk of “le-chatat” — intention must match the specific chatas designation; mismatched intention invalidates.
Slaughter of the individual’s ewe-chatas must be performed with intention for that specific offering. If the kohen (or the owner) intends a different type of chatas — for example, treating a chelev-chatas as if it were a blood-chatas — the offering is invalid. The Torah’s language “as a chatas” locks the intention to the particular designation of this animal.