You can use a Murray breaker in a Siemens panel and vice versa. If you look at the sticker in a Murray panel it says to use Siemens breakers.It doesn't.
It applies to using something that you know is the same but not listed as such in that application.
Can you use a Murray breaker in a Siemens panel, even though they are the same? No.
Can you treat the busbar in a 150A panel as if it's a 225A panel even though it's the same? No.