I'm sure when I was playing on the 1.16.5 server with this that the speeds were changeable as I had a mod that utilised redstone as a fuel, so changed lapis to be just as fast but with a little more durability. But I can't seem to see how to change the speeds for them in 1.20.1. So if this has not been a feature, I would love for it to be added again.

Thanks

It was never a feature. I will have a look at it and might add it to future versions