Is it possible to switch firmware from Homekit to Tasmota

yes it is possible.

Yup, just did the switch from Homekit firmware to Tasmota on a 5050C RGB light controller.

* Download the latest Tasmota firmware from their Github (I used tasmota-lite.bin) to your computer

* Connect the Homekit firmware device to your wifi, find its IP and go to the user interface

* Upload the tasmota-lite.bin you downloaded earlier (choose a file from your computer and hit upload)

* This will leave the device in an unresponsive state

* Reset all settings by powering the device off and on seven times (leave power applied for around 5 seconds each time and leave it powered on the seventh time)

* The device will then be ready for initial setup (It will be in AP setup mode)

* Use the template settings as seen on the athom.tech product page for the tasmota model to configure tasmota

I switched the Plug firmware from Homekit to ESPHome no problem. It was better than with the original, because now it measures the power.