I think you can load kicad pcb files into any editor, and change field values, that may not all be accessible in the gui.

Changing the track width in the Design Rules Editor will not auto update the traces in the design. You need to highlight the traces you want to change and update it in the track properties for achieving the goal.

You can depend on the size of board, which is probably easiest to select them all by holding shift and and clicking on them all then enter in a new width.