Startup application not triggering

I am on Linux Mint on a rather old refurbished Lenovo T460. The enter key is broken, so I want to have the key remapped to my insert key.

Until now I have been using xmodmap, however since a recent system update it no longer works.

Currently this is my startup script: xmodmap ~/.Xmodmap

And this is the contents of the ~/.Xmodmap file:

    
$ cat .Xmodmap 
keycode 118 = Return

! Disable broken Enter key
keycode 36 = NoSymbol

  

Thanks in advantage for the help :)

Edit: I forgot to mention that copying and pasting the command I have in Startup Applications into the terminal and then pressing CTRL+M works, but it is a pain to have to do that every time I boot my machine.