How to easily set a master ID without losing everything?

Scripting
1

Hello. I have a particularly smart person who decided to switch out some masters for some older version. Long story short, I would like to set these masters’ IDs to be the same as the IDs of the masters in my old version.

I tried setting the master ID with:

master.setId_(old_font_master.id)

but then, all my glyphs in the master were suddenly empty and all data was erased for the master. I’m sure I’m missing something, but what is it? Thanks!

2

The master id is used in all kinds of places. The easiest is to do it in the .glyphs file in a text editor.

3

Great, thank you!