When running `rm -rf`, is it possible to exclude certain subdirectories?

Simple conceptually, and has a low risk of error:

mkdir TO_DELETE
mv * TO_DELETE
mv TO_DELETE/var_opt TO_DELETE/var_log .
rm -rf TO_DELETE

Ignore the error from mv about moving TO_DELETE to a subdirectory of itself.

You can also use ksh's extended globs:

rm -rf !(var_opt|var_log)

These are also available in bash if you enable them:

shopt -s extglob
rm -rf !(var_opt|var_log)

Ditto in zsh:

setopt ksh_glob
rm -rf !(var_opt|var_log)

Zsh also has its own extended globs:

setopt extended_glob
rm -rf ^var_(opt|log)

If your input file names are generated by users, you need to deal with surprising file names containing space, ', or " in the filename.

The use of xargs can lead to nasty surprises because of the separator problem.

GNU Parallel does not have that problem.

find /space ! -iregex '(var_opt|var_log)' | parallel -X rm -f

Watch the intro video for GNU Parallel to learn more.