Not as easy as you'd think. This is the issue we face everyday. Users expectations, needs, etc.. vs reality. Some things just can't be done like you want them or even at all. Joomla menu links render and are done, no API, nothing to get to them. We protect the end result, the url, which is how we can protect menu links. We'll have to figure something out to show/hide menu links based on subscription, maybe jQuery, I can't say for sure. It is something we plan to implement into CBSubs (not CB, why CB? This is what custom modules are for.. Please provide an example extension that does exactly this as far as I am aware they do not exist).