Adding new connectors means you only need about an inch extra on each side. Very low skill required if you have the (cheap) tools to do it. Actually putting new wires in place is a bit harder but still fairly easy. Attach some string to the old cable, pull it all the way through the walls. Attach the new cable to the string, then pull that through the walls. Then just add the connectors like the other scenario.

Replacing connectors is east, but won’t solve your problem if the issue is bad cables in the walls. Pulling new cables entirely depends on how well they were installed. A lazy install will actually be much easier to replace, because a lazy installer won’t bother stapling cables in place. They’ll just run the cables across the attic/crawl space and leave it where it lands.

If you’re lucky and got a lazy installer, then you can be equally lazy; The old cable in the wall is going to be your pull line for your new cable. Step 1 is figuring out which lines are which. This is easier with something like a cable sniffer, but there are a few ways to do it. But assuming you know which cables are which, the rest is fairly straightforward.

Use electrical tape to affix the old cable to the new one. Just make a bend on each cable, hook the resulting bends together, then wrap them tightly with electrical tape. The bends hooked together allow the cable to hold the strain, rather than the adhesive on the tape. And you want to use electrical tape because it stretches. Pulling it tight when you wrap ensures that the tape will compress the cables with every wrap. You also want to try to make the connection as “smooth” as possible, so it won’t snag on anything when you pull it.

Now that the old cable is attached to the new, just grab the other end of the old cable and start pulling. It’ll drag the new cable through the wall for you as you pull it out of the wall. Fair warning this is much easier if you have someone feeding the new cable in as you pull, to ensure it doesn’t snag on anything as it enters the wall. It also only reliably works on installs without a lot of bends and corners; Every corner you have to pull around is another potential corner to get snagged on. If you get snagged, sometimes pulling it backwards (tugging on the new cable entering the wall) can help you reset to try again. But sometimes there’s no replacement for good old fashioned legwork; If you get really stuck, or your tape comes undone, or your cable breaks from the strain, you may need to go crawling around your attic to fix it. This is a fast method, but it’s not 100% reliable.

No pulling wires from walls, just cutting the ends off and installing new connectors. Might not be enough in every case though.

Crimping took me like 5 attempts to get right when I learned it in school.