Yes, you could do that.
I'm not sure if it would be better or worse than what you currently have.
But the water comes into the into the canister, it will go over the bioballs/rings and it will get colonized by "good" bacteria.
The thing is though.. bioballs are used in a sump because the water drips over them and you get great gas exchange (Co2 out, oxygen in)
In a canister, you don't get that advantage.
So I Guess you could do what you propose, but I'm not sure why you'd want to do that.. I'm guessing the manufacturer figured out the best
media for it, so why not use what they recommend.. Especially if you are already running that way.