Let’s see here.
If you want to switch between sets of UI elements (as opposed to creating and destroying them) the fastest way to do that is to probably create them all at the beginning of the game - or as needed - and then saving them somewhere without drawing them. You can also recycle elements by changing some of the variables: the “text” variable, for example, more or less does what you expect it to and is generally safe to change at any point in the code.
Regarding the memory leak, it turns out the list of contents attached to each struct wasn’t actually getting deleted (only cleared) in the Destroy() method, which is probably the cause of what you saw - it would only have been leaking a few bytes per element, but if you created and removed a lot of them it would start to add up over time.
I’m not noticing anything immediately unusual about RemoveContent() that would cause a crash, so later on I’ll poke around and see if I can find it. The only thing in your example file is the obj_emu_demo object, by the way.
Once I’ve done that I’ll post an update. I also kinda want to get rid of as many ds_lists as possible, in favor of things like arrays, since currently losing references to elements in other ways without calling the Destroy method will also cause a memory leak. In the meantime - if you haven’t already - add ds_list_destroy(contents); to the destroyContent() method in EmuCore.