Dialog Loading Screen Question

Is there a way to modify the Dialog's widgets while a script is running? I’ve tried using :show{wait=false} and app.refresh(), while :modify{}ing a slider widget in a for loop, yet the Dialog only appears after the script finishes running. I’ve created a LUT generator that limits its colors to a color palette yet takes time to render, which explains the need to develop a progress bar. Thanks in advance for responding.