If you have dishes big enough that you want to use, yes they can be converted. Even an old dish 500 dish will receive some fta signals, but its just an interesting hobby, not really for reliable use. If you have any of the pay-tv dishes that were bigger, like the ellipticals dish had on 121, I think, at one time, those can be converted. You just have to finagle the linear lnbf in place of the circular lnbf. FTA is fun, but for most of us it is a working hobby, not replacement for pay tv though. You'll find a few cable channels unscrambled once in a while but those usually don't last long so we can't get too used to them! The variety is what its about, you would really want a motorized dish, with 20+satellites up there with programming to view...moving dishes manually gets tiresome. The fta signals are much weaker , of course, than the pay-tv birds' signals, most of us use 1m dish or bigger to get good reliability. MicroHD is a nice receiver-will record tv if you add USB drive, and there's a little import called X2 PremiumHD , will also record.
Check ebay , amazon, other places to see what's out there for receivers, post your questions here and somebody will likely have an answer/opinion. Welcome to Satelliteguys!