Can you combine an Artificer's Enhanced weapon infusion with a +3 magic weapon?

Question

The Artificer's Enhance Weapon infusion (ERftLW) grants a +1 (+2 at 10th level) bonus to attack and damage rolls made with the infused weapon. Is it possible to combine this infusion with a magic weapon that already has a +3 magical bonus? Thereby granting a +4(+5 at 10th level) bonus to attack and damage rolls.

I believe it is ok, if you first apply the enhanced weapon infusion and then the +3 from the magic weapon. However I don't know if "(any)" weapon applies to the enhanced weapon (that become magic).

Answer 1

No, per RAW, since the +3 sword is already magical

Artificer Infusions
Artificers have invented numerous magical infusions, extraordinary processes that rapidly create magic items. To many, artificers seem like wonderworkers, accomplishing in hours what others need weeks to complete. {bolding mine; E:RftLW)

And there is another rule under Infusing an Item:

"Whenever you finish a long rest, you can touch a non-magical object and imbue it with one of your artificer infusions, turning it into a magic item." (E:RftLW)

There aren't any rules yet in D&D 5e that modify a magic item. The Enhance Weapon feature as a sub set of the Artificer Infusion feature indicates that the infusion itself does {something magical} and ends up with a magical weapon. Since the +3 weapon is already magical, it isn't eligible for an upgrade. What your artificer needs to do in order to Enhance a weapon is find one that isn't magical, and then make it magical.

Answer 2

Infusions can only be applied to mundane items.

If you look at the description of the Artificer's Infuse Item feature it specifies that the item must be non-magical (Eberron: Rising from the Last War, 57).

At 2nd level you gain the ability to imbue mundane items with certain magical infusions

Whenever you finish a long rest you can touch a non-magical object and imbue it with one of your artificer infusions, turning it into a magic item.

Answer 3

This does not work.

The enhanced weapon infusion says:

This magic weapon grants a +1 bonus to attack and damage rolls made with it.

The weapon infusion specifies exactly what the weapon becomes: a +1 magic weapon.