Thank you, now I understand what it is that you are trying to do.
My first comment is that the switch which you showed in your first post is unsuitable for low level RF use.
Looking at it, it is quite large and is intended for switching fairly high voltages and currents.
The contacts in the switch may not make good contact when driven with low level RF signals.
Also, being a large switch, there will be significant stray capacitance and inductance in the internals of the switch.
As others have commented, a "calibrated" variable capacitor would be a good start.
However, good quality variable capacitors can be a bit difficult to find, and expensive (I don't know how big is your budget?).
For a "quick and dirty" solution, in an experimental environment, I would suggest using D.I.L. switches.
I have used this technique before, switching resistors in parallel with a tuned circuit in an oscillator running around 7 to 8 MHz.
The idea was to measure the effects of resistive loading on the frequency of the oscillator.
It worked quite well.
JimB
Edit
The experiment with the DIL switches was written up here on ETO a number of years ago.
Look here:
A bit of an update on the subject of resistive loading of the tuned circuit in an oscillator. I have been doing a bit of playing around with this today and at a first pass there is a definite change in frequency as the tuned circuit is loaded. It will be Monday before I can devote time to...
www.electro-tech-online.com
to see a picture of the set-up with the DIL switches and a resistor network.