You'll need to call the county assessors office to ask them to adjust the assessed value of the home to include the new guest house. If you have lots that aren't included in the APN you want you'll have to merge the lots together so that they all have one APN. That's not hard to do and I can help outline the process to you. I've done subdivisions and accretion (merging) is simply the reverse process.
As for valuation, an acre in the Country Club area is worth about $1.8 million right now. Your overall valuation would be based on the value of your home plus that land value. If you'd like a more accurate assessment, send me an email or call and I'll be happy to help - no obligation.