[Tomdb]

What year of Subaru are you looking at? 2001-2017 build years cannot get reclassified on fuel type/tax class in the UK.

Also a Subaru, again depending on year will have a bunch of electronics you will need to keep happy for the various systems to keep operating.

 

[Tomdb]

Am curious why the can't be reclassified if they've been deICEd?

Bureaucracy, they way one entity responsible for the database interprets legislation.