Testosterone enanthate is a single compound, a single molecule. If you dissolve it in oil, it's still testosterone enanthate. The ester stays attached unless something specifically removes it like an esterase enzyme. Extreme heat might break down the molecule as well, but that doesn't really apply here. The hormone bonded to the ester is stable in solution.
Tren acetate is the same way. Dissolve it in oil, and it's still tren acetate. Dissolve both tren ace and test e in the same oil, and both will remain unchanged. Nothing about mixing the two will cause a chemical reaction to change the structure of the molecules. A blend containing test e and tren ace will work exactly the same as taking the same dose of each separately.
Most blends are either all short ester (test p / mast p / tren ace) or all long ester (test e / mast e / tren e). That's just about convenience and injection frequency. It works the same way with no ester blends like tne / trne / mtren.