Lotta things mixed together there.
Lemme try to untangle from the beginning …
Yes, there are standard latching and release arrangements for unpowered “dumb” bombs. In the era before airplanes had computers, by and large any airplane was physically capable of carrying any then-current bomb that wasn’t too heavy. Various pylons of various eras had different mechanical weight limitations.
But the ability to drop a dumb bomb usefully included the ability of the pilot to aim it. Every type and brand of bomb falls differently. So back in the day there were reams and reams of ballistics tables from which a crew would compute aiming settings then try to fly their airplane to match the settings then let the bombs go and hope for the best.
If the Brits and Americans or the USN and the USAAF did not have each other’s paperwork (and training) to do that computation they couldn’t usefully use each other’s bombs. Even if they did mechanically fit in each other’s racks. Which back in 1943 they probably did not, but NATO and DOD within NATO has been well standardized on that stuff since the late 1960s.
Once airplanes got smart with their own computers, now to usefully use a dumb bomb your airplane has to have the software module loaded that knows all about that model of bomb to compute an aiming solution. And the UI for the computer needs to have that model of bomb added to it’s list of possiblities. And the pilot needs to be qualified in all that. And the munitions manuals for the people who load them need to be updated and they have to have a bomb truck with a rack that fits the exact shape of the bomb to be able to carry it safely from bunker to planeside. Plus the people who maintain the bombs, assemble the bombs, store the bombs, inspect the bombs, etc. all need the tools and training and books to do that work.
There is far, far more to using a modern dumb gravity bomb on a modern smart airplane than “A fully assembled and fuzed bomb has magically appeared beside a parked jet. Do the hooks and latches fit?”
Once we move on from dumb bombs to either powered bombs or missiles, the complexity explodes. Now the computer on the airplane needs to know all about how to talk to the computer on the weapon. How to awaken it, query its status, tell it “get ready; you’re next”, tell it what to “look for” as a target, receive and understand status reports back from the weapon that everything is good (or not), and then finally tell it “Go get’ em.”
All of that is a big job with a lot of bureaucracy behind it.
So if you see that the F-18 can carry LRASM but F-16 can not, you can assume the issue is bureaucracy and lack of need, rather than some mechanical obstacle. For multi-national airplanes and national weapons it gets even more complicated by national security, national pride, etc. It is a major political whoop-di-doo for e.g. the USA to choose to update their F-[whatever]s to carry some British weapon instead of a competing German one.
As @Chronos said while I was still blathering, there are some exceptions to my general outline above. The e.g. F-15 can carry weapons heavier than the smaller F-16 can. The B-52 can carry weapons much heavier and larger than the F-15.
Nuclear weapons (not that you asked) are a whole different kettle of fish with very complex interface requirements and very detailed certification paths for a lot of specialized hardware that needs to be between the pilot’s release button and the bomb and the bomb rack.
Lastly, as to fuel pylons.
Any fighter / attack type aircraft have what are called “hard points”: the structural accommodations up inside the wings and fuselage to bear these heavy loads. Which also include munitions-related wiring carried to up inside the wing. On the skin surface there will be large female-threaded sockets to bolt the pylon up to. And a small access hatch to open to connect wiring plugs from the pylon to sockets in the aircraft interior. Similar umbilical connections are made to the weapon unless it’s a dumb bomb.
A fuel-capable hard point will also have a fuel pipe ending up inside the wing or fuselage structure and capped off. Which pipe leads downstream towards internal tanks and eventually the engine(s). These are often, but not always, also fully capable weapons hard points.
Typically pylons are installed on hard points and left attached there for months or years. Pylons are themselves a mix of standard connections and internal components for some things and being sized and shaped for the particular spot on the particular airplane they’re going to attach to.
For modern versatile fighters you may find an entire squadron of e.g. F-18s are equipped for long range patrol and ship attack with one configuration of fuel tanks and pylons while a different squadron dedicated to short range air defense of the ship have a different assortment of pylons and tanks. Either could be converted to the other config given a day and a dozen men, but easier to just draw from the sub-fleet that’s already properly configured for the mission.
Finally weapon adaptors and weapons are hung on the pylons on a daily basis for employment.
External fuel tanks in the modern era are generally carried on dedicated pylons that resemble munitions pylons but include the extra plumbing to connect to the tank proper. and of course there’s extra wiring to connect to the fuel gauge system and extra plumbing to also carry some kind of pressurized gas into the tank to help force the fuel out. That’s often bleed air taken from the engines or the HVAC system.
External fuel tankage back in WWII was sorta standardized within any one service, net of the major technological advances in just the 5-10 years the war lasted.
Nowadays external tanks tend to be highly optimized for the individual airplane with the right size, shape for aerodynamics, capacity etc. So while one might be able to physically bolt an F-15 external tank & pylon onto an F-16, you wouldn’t want to and it probably wouldn’t work.
Some concrete examples from the era I’m most familiar with. The classic F-16 as used by USAF has 9 hardpoints: numbered from left to right. The outermost (#s 1 & 9) are on the wingtips and can carry air to air missiles only. The centerline (#5) can carry a (singular) large or small bomb, a (singular) large fuel tank, or a large ECM pod.
The inboard wing pylons (#4 & #6) can each carry a smaller fuel tank or a variety of large or small bombs or additional multi-racks that can themselves carry multiple medium-or-smaller bombs or air to ground missiles. Or air to air missiles.
The mid-span wing pylons (#3 & #7) can carry the same as 4 & 6, except no fuel tanks.
The outermost pylons (#2 and #8) are physically different from those attachable to stations 3, 4, 6, & 7, and can carry either a singe air to air missile or a multi rack with a couple of small air to air missiles.
