Thanks everyone for the safety valve info. I very much like the Paula solution, and the silicon clad washer is now on order.
As for the swap question, when I opened the box the engine shipped in my wife's face lit up with a smile. I'm fairly certain she has laid partial claim and a swap would be difficult. However, there's no telling what the future holds.
P.S.
There's a Fleischmann in my future. From the pictures, it looks to be in decent condition, but I'll know for sure when it arrives. It'll round out my modest collection at 4 engines (I hope), which is what I have room for.
I so appreciate the size and weight of model steam engines, as they are much easier on the back than the hit and miss engines and other heavy iron I used to dabble in.