I tried this and you are right, you can't do what you want to do.

So here is my way of getting it to work.

First. There are two listings of MAGEE, DO NOT remove/delete either of them.

To maintain a T/D and a vertical path, I changed BOTH instances of MAGEE to read 180/3380. If I change it to 180/3000, then I lose the T/D and the vertical path. So to get around this, you can use a FLTCH down to 3000, instead of letting the VNAV only take you down to 3380/3390 feet. Because 3000 feet is below the vertical path, once you arrive at that altitude, the A/P will then use ALTITUDE HOLD and SPEED, but at least it will work.

Hope this helps

Mark