Trimming a Futaba servo lead to fit a JR plug
See wire braiding to learn hot to remove the servo lead.

Trim the servo lead on a surface you don't care about. Be careful as you can easily expose the pin so just trim the major piece off then sand it flat.

Sanding the Futaba servo lead to fit a JR plug
You want to sand just the tab off of the servo lead without taking any material from the side. For servo extensions you will have to get it very flat.

Reinstall the servo lead with your braiding and heat shrink installed and then get your heat shrink in place while still allowing the heat shrink to move on the wires.