Is it possible...

[M4J0R70M]

to have MULAB 5 style slinders (round-handle) in mulab 9?

[mutools]

Yes, have a play with MuLab menu -> GUI -> Vertical Sliders

[mutools]

Quick tip to get close to M5 style sliders:

1. MuLab menu -> GUI -> Vertical Sliders
2. In the Vertical Slider frame, lower Handle Size to 14
3. Select the "Handle" layer and set Layer Type to Circ. Value Handle
4. Select the "Handle 2" layer and set Layer Type to Circ. Value Handle
5. Mute the "Value Line" layer
6. Click Apply