As root you should be able to read and write all files. The exception is remote files shared over a protocol like NFS, but those will most likely appear to be readable/writable until you actually try.

For example:

# id -u
0
# ls -ld noperms
----------    1 sgifford sgifford        0 Jul 30 23:37 noperms
# perl -e 'print STDOUT (-w "noperms" ? "" : "un") . "writable\n";'
writable

What sort of problem are you running into that requires you to do this?