[Flac] re-encode

[Richard]

Have some flac files, that I've been trying to re-encode again...

example:
abc.flac ( was coded at --fast ) and its huge
so,

flac -d --best abc.flac
or
flac --best abc.flac
or
flac --best abc.flac --force

NONE of these work, to re-encode the file into --best
file size has not change.

What is the correct command line to correctly re-encode a file to
--best (regardless) on what compress level used before (without )
losing tag information.

TIA ++
Richard