Hello,
Unless you're rooted or got the XPosed Framework for your phone, you won't be able to change anything on this side.
Also, why do you want to edit this? Safe mode is made to avoid eventual device dysfunctions caused by user installed apps, so editing this is not a good idea.
However, if you still want to do that, you can use an app to push the app(s) you want to be added to this safe mode list as system apps. This is the only way I see.
Keep in mind that it's really not a good thing to do...