actually, you can use any non-tied property to invoke an arbitrary Nasal callback - thus, you could use a property-rule to regularly invoke Nasal code, or modify a non-FDM property via a FDM system/component - that way, you will end up calling Nasal at FDM rate.
We've actually had a number of debates regarding this, including some with patches - For instance, see:
Actual programming language for autopilot implementation?
However, to be honest, you seem to be asking many fairly basic question that you could answer for yourself by spending a few hours going reviewing the wiki and other docs - e.g. a property that is invokes a listener is automatically also calling a callback function. At this point, it seems that you really need to do some reading to really understand the advice you are given - Thorsten basically answered all your original questions, but you apparently weren't able to process his feedback.
Anyway, once you do a little more research, you will also find postings and patches I shared on the forum to do exactly this sort of thing, including C++ code, i.e. dedicated SGSubsystem modifications