i am almost 100% sure i can replace like for like to a hyperglide Acera, STX-RC 7spd freehub. This is only 30mm so you can only use it with 7 speed. I am curious if you can swap it with a more modern wider one...i think they are ~35mm (even if i had to use the inner spindle interface from the uniglide).

That would allow me to run 8/9 speed or even 7 speed with a 4.5mm spacer behind the cassette.