argonlefou's method works for me.
Hyperspin doesn't appear to be the problem of Alt-F4 not being recognized. That appears to be an issue with Supermodel (it is not unheard-of for some programs to not work with AHK input shenanigans) I tried supermodel, and couldn't get it to close either by sending alt-F4 when "4" is pressed. Using argonlefouou's method, however, did close Supermodel. I didn't use Hyperspin, I just ran supermodel from the command line after loading an AHK script that simply consisted of
4::
Process, close, Supermodel.exe
ExitApp
I see you already have a "process, close, supermodel.exe" line, but are you sure it's getting there? It's outside a block you defined with some braces. I don't know if that's valid AHK or whether it's some kind of HS extension.