The capillary is the small regulating tube if you cut it with side cutters it may partially seal keep this side of the system on the high side so you don’t loose all the oil.
If the cap tube is on the low side it will spray oil at what ever pressure It is charged to.
If it partially is sealed and a slow release this helps prevent the loss of the oil that a rapid release will pull the oil out.
If it seals because your cutters use pliers and squash the cut tube by crushing 90 degrees to the cut this usually opens the copper enough to vent.
What I mean by 90 degrees , from the cut turn the tube or rotate players 90 degrees and compress the smashed together part
use safety glasses as some times the oil vapor and oil come out at great force and have plenty of ventilation as mentioned on other posts.