Thanks for your precisions.
I was thinking that one of the simplest way to do it can be to simply and directly plug the CC2500 on a 3.3v arduino and power it with an external regulator, but I'm not sure de TTL level will be ok for the NRF24 !
It should also be ok using a 5V arduino and a 4 canal IIC I2C Logic Level Converter Bi-Directionnel Module 5 V à 3.3 V (https://fr.aliexpress.com/item/Free-shipping-1pcs-4-channel-IIC-I2C-Logic-Level-Converter-Bi-Directional-Module-5V-to-3/32670479389.html?isOrigTitle=true).

Very intresting : How to give a second life to my old LivingColor !
One question : Is the shield mandatory ? Can I wire the CC2500 and the NRF24 directly on the arduino ?
And finaly, does a chip like this one (https://fr.aliexpress.com/item/Free-Shipping-MD7105-SY-A7105-2-4G-Wireless-Transceiver-Module-3-3V-Better-Than-CC2500-NRF24L01/32714119016.html?isOrigTitle=true) will work with CC2500.h library or should I take one like this one (https://fr.aliexpress.com/item/CC2500-IC-Sans-Fil-RF-metteur-R-cepteur-2-4G-Module-ISM-SPI-D-mo-Code/32674039629.html?isOrigTitle=true) ?
Thanks