Yup, the smaller engine is rated at the same horsepower as the larger. And on your Hobbistar, the 46 will probably haul the sucker about the same as the larger engine can. There are two details however...........

The difference of 6 less ounces of engine weight will have an effect on how the model balances. So if all you do is swap the engines and tank, the CG of the plane is going to move aft. You need to check the CG now. If it's already toward the rear of it's suggested range then you need to be prepared to move the battery forward. If there is no room to do that, then you are going to need to either move servos or add weight. If you have to add weight, ask yourself why you're doing this. You shouldn't just let the CG change and see what happens next time the model flies. You need to deal with it before, not after.

Also, the two different engines swing different diameter props. The larger engine's larger prop can give more thrust. Not always, but usually. The prop diameter is the major player in how well the engine pulls the model. But put identical horsepower to different props and you don't always see different thrust. But it's not possible to predict. So be prepared for possibly a bit less thrust. You'll see it, if it happens, on takeoff first. The model may take longer to get airborne. It may not climb as well. But don't make your judgement on one takeoff and climb. Make sure you have a good needle setting and then try a couple of different props. And don't expect to get full power out of a brand new motor.