Yes. God can make something else better than each thing made by Him but God cannot make a thing better than it is itself because the addition of a substantial difference in definitions is after the manner of the addition of unity of numbers.
For example, He cannot make the number four greater than it is; because if it were greater it would no longer be four, but another number.
When it is said that God can make a thing better than He makes it, if "better" is taken substantively, this proposition is true. For He can always make something else better than each individual thing.
And He can make the same thing in one way (i.e., over and above the essence) better than it is, and in another way (i.e., of the essence) not.
If, however, "better" is taken as an adverb, implying the manner of the making, then God cannot make anything better than He makes it, because He cannot make it from greater wisdom and goodness.
But if it implies the manner of the thing done, He can make something better; because He can give to things made by Him a better manner of existence as regards the accidents, although not as regards the substance.
The universe, the present creation being supposed, cannot be better, on account of the most beautiful order given to things by God; in which the good of the universe consists. For if any one thing were bettered, the proportion of order would be destroyed; as if one string were stretched more than it ought to be, the melody of the harp would be destroyed. Yet God could make other things, or add something to the present creation; and then there would be another and a better universe.