I tried googling around, but didn't find the answer.
I have a AC outlet with a remote controller, working with 433.92 frequency and I have TR120 & HDR120.
I was thinking, if I can somehow change the frequency (&hack later to use bluetooth/wifi to control things)

 

The transmitting frequency of most low cost remote control transmitters at and near that frequency is determined by the properties of a Surface Acoustic Wave resonator. If your transmitter has one of these, then you can change the transmitter frequency by changing the SAW resonator.

SAW resonators come in a variety of metal and ceramic packages but the metal cans are the most common in low cost remote control transmitters.

You should be careful to not move your transmitter out side the band in which its operation is permitted. In some jurisdictions modifying the circuit might be illegal.

Higher-end transmitter (read that: designs after about 1995) use frequency synthesizers most of which use a fixed ratio of transmitter frequency to the frequency of the reference crystal. In those transmitters the reference crystal can be changed or it can be loaded with extra capacitance to shift the frequency, and the frequency shift will be multiplied by the synthesizer.

If you can show the schematic of your transmitter, or even a photograph of it showing the components you might get a more certain answer.

If you change the transmitter frequency, then you will probably need to adjust the receiver frequency.

 

...
If you can show the schematic of your transmitter, or even a photograph of it showing the components you might get a more certain answer.
...

Thank you for your response!
I rechecked the TR120 and it seems that it needs to go for another project, it's using FM instead of RF !
( https://www.cnet.com/products/sennheiser-wireless-rf-with-charging-cradle/specs/ ) I don't know why I thought other...
Although, I can't find any information about the headphones itself not being RF.
( https://www.amazon.com/Sennheiser-RS120-Wireless-Headphones-Charging/dp/B0001FTVEK )

The remote control for the sockets is:
http://www.clasohlson.com/uk/Cotech-Smart-Home-Remote-Switch-3-pack/18-1255
( I think the socket's are a little different - 2 holes)
And about the remote control, I think ordered from X and placed their 'manufacturer' name on it (not sure how this process works)
I couldn't get more info about the remote control, but I can always open it up if it helps?

 

FM comes under RF (radio frequency) term

 

FM comes under RF (radio frequency) term

Right, FM can be used with any type of communication media where there is a carrier frequency.

https://en.wikipedia.org/wiki/Modulated_ultrasound