I was scared of it not venting properly if it was seated in the old cap like sealed in. What I did with mine is drill a hole in the base of the old cap,solder the new cap in place by wrapping wire the through hole leads on the solder posts on the bottom, then I put epoxy putty around the perimeter from the bottom, and poured liquid epoxy in maybe 1cm deep from the top (so a segment of the top was flooded with epoxy). This way the new cap was firmly anchored in the base of the old cap (with glue on the swaged area) but the top was completely unrestricted so it can vent properly.
Granted you lose most of the can if you do this and it looks weird. If I had to put the old cap in the new cap and have it look original, I would cut a big hole in the top of the old cap and glue in a stainless mesh from the bottom, so if it vents it can vent nearly freely.
but mine had a solid metal top (it was a solid metal can). IDK if you have some kind of plastic baffle there?
I know for a fact that potting capacitors totally is a recpie for shockwave during failure, you are supposed to put a tube over it so the vent can breach freely. The burst disk is designed to vent it gracefully, if you obstruct that it goes boom
I am curious how well a tinned copper mesh would solder to the capacitor body (mine was not shielded like yours) if you actually wanted EMI shield. It should be good to the GHZ with a fine mesh that is soldered or conductive epoxy on.