Iirc, yes, you will keep the patterns you already have. I haven't tried it myself (every time I get to like 100 basilisk eyes I want to gouge my own eyes out because it is just so goddamn boring) but I think it said somewhere in Wowhead comments that the already known patterns stay untouched.
You can't learn a pattern you bought unless you meet the requirements but you don't lose already learned ones. I was Scryer and switched to Aldor and kept my recipes.