Re: CYA too HIGH?
You don't need to completely drain the pool, just mostly. Leaving 3" to 4" of water in the pool will help keep anything from shifting and make the whole process a little safer.
No CYA test is especially precise at high CYA levels. So your actual CYA level might be a lower or higher.
You should also think about how the CYA level got that high, probably from the use of trichlor tablets, and change your practices so you don't have the same problem again next year.