As others have pointed out, memories are extremely fickle. Fickle enough that I do not think it could be feasible to have any kind of fine-grained control over what to delete or replace. It'd be a bull in a china shop.

I think the only way it could potentially be done safely and properly is with a computer several orders of magnitude more powerful than a human brain, capable of copying the patient's brain, running all kinds of simulations on it to figure out how to make the exact changes without touching anything else, then writing those changes back to the host. If we're talking eventually, that could be an eventually, but a very very big eventually.