That varies between models and the site makes a good effort to outline the least possibly damaging way to do the mod for each model. For me, the spring is just sitting on a hook without a fastener, there is a mechanism that when the key is pressed the spring pulls the drum over by a tiny amount, the spring is under tension when the carriage is slid all the way to the new line mark and it reduces every time a key is pressed. In my original comment I posted the site with the instructions. I will say that there are some models that require bending a strip inside but mine did not require that step.

Edit: I had not looked at them in a while and some of the modded typewriters go for three to four times as much as their unmodded siblings. My Royal is 1200$ on some pages I'm seeing.