What was with the switching between uniforms in Generations?

Perhaps it was "casual Friday" and crew could wear whichever style they personally preferred.

 

Ah, but weren't the DS9 uniforms designed for TV? How is switching one set of TV uniforms for another any better?

 

Actually, I'd say that the presence of the "belt" argues just the opposite - that the uniform was made for someone of greater girth than Stewart and the strap was needed to make the garment appear better fitting!

 

But then there would be visible creases down the sides of his clothes where the fabric was bunched up.

 

Maybe it was only a little too big? The belt certainly does the job of shaping his waist more.