I'm creating an artificer subclass that has features that alter existing infusions. Is there any way to create a check box to add a trait to a particular item? For example for hexblade checking a box to indicate a weapon is a hex weapon. I created from a hexblade and did not see how that was done. I would love if there was a way to directly alter infusions, but I doubt that's possible.

It is not currently possible.

The Hex Weapon box is accomplished by adding a feature named “Hex Warrior” to a subclass. But all it does is that one thing, it cannot be altered.