Not recommending that anyone do anything unauthorised, but more as a comment - as teenagers with first cars, we used to use the same flairing tools to make new brake lines for our old rust bucket vehicles. In many ways, equally as dangerous if you got it wrong, with consequences for both you and others. In both cases, test each join for leaks.
As for gas, well every time I change the bottle, there is a possibility of not making a tight connection and gas leaking - in some ways, even more likely of a small leak with the gas fuse fitted given that introduces another join nearby that could get worked loose each time it is disturbed. The reason I again use soapy water to test each time (a couple of months ago, found that a swap and go bottle must have had a slight fault in the screw part of the valve - although not noticable until saw the soap bubbles, tried and tried to remake the connection even on another gas tail but leaked each time - took it back to the shop for another bottle and they marked it as faulty).
I'm happy with my new rear gas bayonet......