Components are parts of the system that you absolutely need to get sound out of it. In a conventional system, source component(s), amplification, speakers, ICs, SCs, and PCs.
Beyond that everything else, categorization-wise, is subjective.
Accessories are items that started off as tweaks but have become sufficiently mainstream to be thought of as pretty standard, e.g. footers.
Tweaks aren't mainstream, e.g. mpingo discs.
One man's tweak is another man's accessory.
Fashions change, and generally there is a trend for less out-there tweaks to come to be thought of as accessories. It's an on-going process. A good number of tweaks never make the grade and fall by the wayside, only to be recalled years later in nostalgic threads on Audiogon.
Beyond that everything else, categorization-wise, is subjective.
Accessories are items that started off as tweaks but have become sufficiently mainstream to be thought of as pretty standard, e.g. footers.
Tweaks aren't mainstream, e.g. mpingo discs.
One man's tweak is another man's accessory.
Fashions change, and generally there is a trend for less out-there tweaks to come to be thought of as accessories. It's an on-going process. A good number of tweaks never make the grade and fall by the wayside, only to be recalled years later in nostalgic threads on Audiogon.