These "Slap Yo Momma" tools, or any of the comparable filling tools will save your o-rings! Very easy to use!
Also, I now drill my carto holes... Punching them with any tool, be it a saddle valve or purpose designed carto punch, was distorting the body too much and made it way too difficult to get the punched area
through the o-rings...
Some folks slot their cartos, but I find it's too easy to go overboard. At least with a drill bit you know exactly how big the hole is going to be.
I use a tiny little bit in a dremel tool on one of those little dremel workbench drill press adapters, and have my carto in a cradle to keep it from moving around. A bit over the top for a little hole? Yes... LoL! I'm a perfectionist...