Can I put a CM3 in a A04 Devterm

Yes, the cores are swappable. If you get CPi’s carrier board for the CM4, you can put a CM4 in it, too. The R01 is a RISC-V chip (Allwinner D1), not even ARM like the A04/A06 and works in the same hardware, the uConsole and the DevTerm. It’s really cool, I have swapped cores between devices.