That post is two years old. From the HTTP Binding documentation itself:
Transformations can be chained by separating them with the mathematical intersection character “∩”. Please note that the values will be discarded if one transformation fails (e.g. REGEX did not match).
This is all about transforming the incoming values at the Channel level, before it is passed onto the Item via its link.
Note that you can use the REGEX transformation as a filter. I’m rubbish at REGEX so am not sure if it’s possible, but perhaps it can look for values within a certain range - if it doesn’t find any it will fail, and that particular value will be discarded, and no update is sent to the Item. Or, as you say, somehow fail if it finds the specific massive number.
An example here, for the MQTT Binding. Syntax is the same for the HTTP Binding, though the binding’s parameter has a different name.