How stable is the Mac OS version of Armory?
Has quite a few UI related issues still. We recently got someone full time on it so the future is bright on that front.
If I wanted to set up an offline wallet, and I need to assign a "watching-only" wallet on a computer that already has a wallet, how do I change it?
Once that is done, how do I remove the key data from the watching only wallet once it is converted (assuming the old wallet had key data on it)?
Not too sure what you are describing here.
This is how you should be going about it anyways: Create your wallet on your offline machine, create a paper or fragmented backup, verify the backup, then create a watching only wallet of your wallet and take that your online computer.
You can outright copy WO wallet that file to your datadir or import it through the import option.
If you have a wallet which private keys have been exposed to the network for a long period of time I'd suggest just moving these funds to a proper offline wallet. You can get rid of the private keys through Armory. Pick Delete/Remove this Wallet in your wallet properties window.