No. Large polyped stony corals usually tolerate it, but small polyps and xeniids definitely do not. You'll kill 'em all. What are you trying to do? The only thing that a freshwater dip would do to live rock is possible get rid of flatworms or cyanobacteria...If you really must I guess you could pluck the polyps off and try to reattach them at another site, but you'll lose some.