Based on my own experience, they're definitely not interchangeable. Went through something very similar to what you're describing, so you're not alone here. Honestly still working out the smartest way to tackle both issues together.
Once I started reta, hunger control turned out to be a relatively small piece compared to the mental food chatter. Around the three month mark on reta is when that chatter finally began fading. Still got the occasional pull though, so added cagrilintide to shut it down completely. Barely noticed anything at .5mg during that opening week so raised it to 1mg alongside 5mg reta. Yesterday's food intake was just coffee, a protein drink, and a quarter portion of my noodle soup. Zero hunger the whole day, and whenever I did eat, fullness hit immediately, not great if you're trying to hold onto muscle.
Anyone claiming cagri never triggers hunger is probably running a higher dose than they actually need, same mistake I made. Can't speak much to tirz, never really dug into it, but don't hesitate to test things out. At the end of the day we're all running our own experiments, tweaking numbers is just part of the process. Good luck out there