I played with that idea a few months ago and it seems impossible to measure things like this without having some kind of detrimental effect on the circuit. Sure we can have a probe with impedance of much larger than the system impedance, but that probe also has capacitance which is significant above a few MHz. I noted this effect when I built the FET probe from Troubleshooting Analogue Circuits. It could change filter response and VFO drift even when probing low impedance portions of circuits.
Fortunately I'm not limited to reverse engineered systems here where someone else decides the impedances so I'm basing my forward engineering work purely on 50 ohm blocks and substitution based measurements. Start in LTspice, prototype, build, test, integrate. This means that the measurement system has the same load on the system as normal duty and therefore no side effects (well not quite but it's far closer to ideal).
RF probes are horrid. That's what started me on this journey. They're good for finding if there is a signal but not how big it is. I'm not sure how you can do any reasonable receiver measurements with one.
Please note I'm drunkenly bumbling my way through this. I might be discovering obvious things on the way that professionals are already aware of. Or more likely completely missing the target
