MC-99793 and MC-48826 seem to have resurfaced.
Since these issues were marked as closed and are at least 5 major versions and two years old, I figured it was appropriate to open a new ticket for the issue. Apologies if this is incorrect.

I was attempting to create a resource pack that overwrote the default music discs when I noticed that using the "replace" tag in the sounds.json file has no effect. Originally I thought it wasn't working whatsoever, but at one point I inserted the record repeatedly and noticed the sound I wanted to play all the time started playing. I then removed and reinserted the disc a few more times, noticing that it would alternate between the two tracks. 
Then, taking this further, I replaced the default button press sound with another one to see if it was affecting more than just music discs.

It seems as though they both just have their default "weight" if I'm understanding the wiki correctly.
You can recreate this issue by creating an empty resource pack with only a assets/minecraft/sounds.json inside containing the following:

// {
	"music_disc.ward": {
		"sounds": [{
			"replace": true,
			"name": "records/11",
			"stream": true
		}]
	},
	"block.stone_button.click_on": {
		"sounds": [{
			"replace": true,
			"name": "dig/stone1"
	}]
	}
}

Then load up a creative world and grab a jukebox and the "ward" disc, attempt to play it repeatedly, as well as place and press a stone button quite a few times.