[According to St. Augustine] nor do our sense perceptions come about because physical objects cause changes in our souls; material things cannot causally affect the soul. The human body is the instrument of the soul, and when it experiences the influence of external bodies, the soul turns towards what is happening in its body, and in this way comes to know the material world. Thus the soul is always active in our acts of cognition. - Leszek Kolakowski, Why Is There Something Rather Than Nothing?, p. 58Hence, acquiring beliefs, at least about material things, does not change any intrinsic property of the mind. And this strikes me as an idea well worth resurrecting in general for several reasons.
First, and least importantly, this would allow a dualist not to worry about the slightly harder half of the mind-body causation problem, the problem of how matter has the power of affecting the soul. (I don't find mind-body causation to be much of an issue at all--as Hume has shown, it's no less a mystery how one billiard ball makes another move than how a mind moves a body--so this consideration is not a big one.)
Second, this has to be basically how God's knowledge has to work given divine simplicity (otherwise God is going to have different intrinsic properties in different possible worlds, corresponding to the different knowledge he has there), except that instead of God's being turned towards what is happening in his body, he is turned towards what is happening in the created world of contingency. So a traditional theist must give some account like this at least in the case of God.
Third, this would let dualists give a greater role to the body and the brain, and indeed would let brain states enter into the truthmakers of claims such as that x believes p. This is good, since it might help with integrating dualism with neuroscience.
Fourth, the idea that x's believing p is grounded at least in part in an intrinsic property that x has and which she typically would lack if she didn't believe p is something that internalists and typical externalists agree on, something that is not a point of dispute between materialists and substance dualists. Now that most philosophers, even ones who widely disagree in an area, agree on a doctrine is not evidence for the falsity of that doctrine. But it is evidence that the doctrine should be examined!
And, as a bonus, this might lead to an argument for the natural immortality of the soul.