I clearly don't recommend your to do so. Instead, I would add some functions in your standard Matlab path which returns your constants. Then, it will be accessible from any script/function/class you (and only you or the persons with your library) will create.
you have a variable which gives you the 0°K in °C:
function k0 = zeroDegKelvin()
k0 = -273.15;
If you do so. I would recommend you to create a toolbox from your function lists or to use git/svn/... to have them on a server. That way, you can easily install your functions on another pc or after a installation refresh of yours.