You can imprint aspects from clearing a dungeon an infine amount of times. The roll you get will be the lowest possible though. Imprinted aspects are not removable by extraction, but they are overwritable by imprinting. The sacrificial aspect isn't only imprint able on a weapon though. You can imprint it to 1h, 2h weapons, gloves, rings and amulets. https://hardcoregamer.com/db/d4/d4-sacrificial-aspect-diablo-4-database/446907/

You can extract aspect from legendary items and they will be stored in Consumables tab in your inventory. Doing this destroys the item. From there you can imprint it on a other item when needed but you won't be able to extract it again. I haven't tried imprint new apsect on another legendary item yet. If it's possible I would assume it would overwrite the existing one. So you'd lose it.

You should be able to imprint the aspect on a ring or amulet too. You can imprint dungeon aspects an infinite number of times.

You can extract the aspect from your current weapon and it'll store it in your bag under the aspect tab. I think it destroys the weapon in the process though, so be sure to have another weapon handy.

You usually find better stat aspects on legendaries anyway.