Some topic communities have very low member and post count and exist across various servers under various names. Can i add single post to lets say 4 on-topic communities or is it considered a bad idea. I am aware that I may be searching across different servers and communities so the duplicity is not ideal, but in terms of exposure in small communities, I would really like to do said duplicity.
Use the crosspost feature. Some frontends can even filter out those someone has already seen.