My daughter sent me a recipe for gingerbread biscotti which has macadamia nuts and then dipped in white chocolate. The recipe says to "melt according to the instructions on the bag". Well, there are NO melting instructions on this bag of Ghirardelli White Chocolate Chips. After reading umpteen stories online about the hazards of melting white chocolate, NONE of them mentioned adding cocoa butter. Is it because most people don't have cocoa butter on hand (I use it in my soap making) or is it that it doesn't work?
White chocolate melts smoothly if there's nothing wrong with it. While I'd sometimes melt milk or dark chocolate in a microwave, for white chocolate I always use a bain marie, heated gently and stirred very gently.
If you try to heat it too fast it will catch and never melt. This can also happen if it's old, or has been stored in fluctuating temperatures.
There's a lot of cocoa butter in white chocolate anyway so adding more wouldn't do much to the melting. It might however be desirable to make the chocolate less sweet.
Proper white chocolate chips are almost all cocoa butter anyway, no need to add any more. If you really need pure cocoa butter, you can buy that in chips too. But if you want the formulation of white chocolate (with some milk solids, sugar, vanilla, etc.) that is sold as "white chocolate", then it makes no sense to dilute it with more cocoa butter. Also, if you do that, the final product (after hardening) will have a different texture.
What I suspect you may have read are failed attempts to make liquid-and-white-chocolate mixtures. Just like dark chocolate, if you add too little liquid, you get bad seizing. But unlike dark chocolate, if you add too much liquid, the whole thing won't set at the end the way standard ganache does. Many people are not aware of this, try doing it with arbitrary amounts of liquid, and get bad results. But if you melt the pure chocolate chips over a water bath and don't let anything burn, you shouldn't have a problem.