Local | Toggle "Assume Unchanged" and Local | Toggle "Skip Worktree" already do what you want.

OK, then I change this topic to be Mercurial-specific.

This is no purely local operation and hence would take a significant time.

See also http://smartgit.userecho.com/topics/86-clickable-urls-in-commit-descriptions/.

You already can do that in the preferences.

Just clone the repository without submodules. Then you can initialize them selectively.

http://smartgit.userecho.com/topics/124-repositories-view-group-in-group/

This could take some time and the refresh performance would become worse.

There is no way to determine from the locally available information whether a tag is local only or exists in a remote as well.