I am in almost the exact situation. I have ringtones already on my phone and I want to keep them!! (on a side note I also want to keep my play lists too) When I went to sync my phone TO ADD new material -- not remove anything -- it wiped it all out. Everything. So I stripped my phone down and started from scratch and pulled it all back from iCloud. Well most of it, it screwed up my one playlist.
I have a 64 GB iPhone and I really want to use all that space but cannont because I can't sync the friggin' thing. I want to KEEP my ringtones.
I tried to "create" more, but iTunes won't take them. I followed instructions on "how to" make a ringtone with songs you already have. Nope. I tried downloading a ringtone from a website. Nada.
iTunes 11 doesn't seem to allow any addition to the ringtone library. Yes, it's there I can see it but I can't add to it.
I would have to see exactly what your trying to do, but i would suggest a free ringtone creation app... (itunes purchased ringtones can only be downloaded once.) If you use a ringtone creator (which is what i have done) you can email it to yourelf - drag it it into ituns and it "should sync over" if syncing is not performing correctly you can reset your sync services.