Retrofit a Hi-Fi remote with a RF 433 MHz module
Yes there's a good chance that the 38 kHz modulation works directly with a 433 MHz transmit module. It so happens that both IR and 433 MHz use the same OOK modulation at 38 kHz. So I would say that it would not work if you removed the 38 kHz signal !

A simple receiver module (BTW get one with an AGC on it like this one)
will get rid of the 38 kHz for you, the same as that the IR receiver (which is currently in your AVR processor) will do.

I think you can just replace both transmitter and receiver and it should just work. No additional filter is needed.