Ferrite cores used as chokes only affect the outside of a cable, not the inside. So, there's very little likelihood of their use affecting most circuits. I think that as long as the cable isn't breached, they won't do any harm. Want to see what happens by putting them on a cable? Do so while watching for 'normal' operations of whatever that cable affects. If you notice any unusual behavior then stop whatever it is that you're doing. I'd also observe any precautions that are normal for whatever the circuit is. If that cable handles high voltage for instance, then I'd be sure that you didn't do anything to get you 'into' that high voltage, or it into anything else. It's not just about high voltage, but that is a pretty fair example, you know?
Most of the uses of ferrite chokes deal with RF. In that regard, it almost always takes more of those ferrite chokes to do what you want than you may believe. I joke anout having a 5 gallon bucket of them, and unfortunately, sometimes it seems like it'd take that many to have any effect.
And then there's the fact that all ferrite isn't the same, most cores are made from a particular 'mix' of ferrite. Different mixes are better for different frequency ranges. I have no idea what most cores are, they aren't always labeled. So if two, three, or four aren't doing any good, it's a reasonable assumption that they aren't the right mix. Or, it takes more than you've used.
Does that tell you what you need to know about the use of ferrite chokes? Good grief no. B ut it can give you an idea of what you can chek to make them work 'better'.
This 'stuff's a lot of fun, ain't it??
- 'Doc