I need to reference another mod in my mod

After learning how to use the tags for recipes, i am facing a big challenge and that is that I have two procedures that I am not able to solve in any way.

First I have a block that I would like to change to another block when right clicking with a custom object from another mod, and I can't find a way to reference the other mod, I thought the tags would help but apparently they only work for recipes, because it doesn't detect the other mod's object in any way.

And second, in the same way, I would like that when an entity from another mod dies, a specific object of my mod will drop a drop from my mod, but I can't make reference to the other mod either, I think that in both cases the other mod is not detected or I don't know What's wrong, I'd really like help.