If you trim the old 50's they will start to get tatty super quick, and you will be back at square one.
Seriously, bite the bullet and buy the Bac brewing screens. They will last you the rest of your life.
They are sent via DHL and take less than a week to arrive from Italy. The transport is expensive so order anything else you might need for your Braumeister for the rest of your brewing life. I got the increase disks as well as the malt pipe screens for my 2 x 20-liter Braumeisters. Also 2 of the hop spider mediums along with the kits for adapting to the Braumeister. I have never looked back. The brainbox who designs and fabricates the stuff, Francesco Taboni, is a cool guy and is generally good and quick at answering any question you may have.
https://www.bacbrewing.com/en/11-parts-for-braumeister-20-liters