Manual Apeture Settings with the 500D

[DesmondMiles4444]

Hello Guys,
I'm new to ML but couldn't find any clues about how i can set the Aperture on my 500D manually during filming or if there is such a setting anyway. I know there is a Trick with mounting and unmounting the lens but this is a pain in the ass considering you have to repeat this procedure again and again. I would be happy about any Trick advise or Tutorial.
Thanks in advance