Of the 12 or 13 pin-locks I have, there is a variety of length in the pressure/gas side, ranging from 2" to ~.33" (basically enough for a flare to hold the o-ring), all of which I am confident were done by a cola company.
To answer your question, yes a pipe cutter would work fantastic!! Also a dremel, a cut-off wheel, basically anything that would cut it would would be fine. You could also pour a pint (or a few) until you got your liquid level below your pressure side tube.
Some of my lids for my pin-locks were retro'd somewhere along the lines from the cola company with the same pressure relief valves found on most push locks, but most of mine are with the preset emergency type blow offs - just be careful when pushing the center down you don't get something in there too deep and gouge your o-ring on the poppet valve.