How to change default settings for all profiles?  

You can't change the defaults.

You can change any settings you desire and then save the profile with a new name...

So a quick way might be to save a copy of each, navigate to the print profiles folder and then run a script on all of them, the content is in 'variable = value' text settings, one per line...

But it would probably be quicker by hand.

Cheerio,

RE: How to change default settings for all profiles?

There is a way to do what you describe, but it is a manual process. I find the effort worthwhile, but you may not. 

I like to make changes to print, filament, and printer settings across 3 different printers, each with varying nozzle sizes and filaments. What I do is this:

1. Create a baseline profile (e.g., a baseline profile for each printer, a baseline profile for filament types, a baseline profile for print settings). This involves cutting & pasting preset settings into a text editor.
2. Create variations using PrusaSlicer's inheritance feature. This involves adding an 'inherits' line and changing the few settings I want to vary between presets.
3. Import the resulting configuration file(s) as a configuration bundle into PrusaSlicer.

You're welcome to check out my configuration bundle for the Mk3 printer here. I've captured my notes on everything I know about PrusaSlicer configuration here. Obviously, this isn't ideal, but this is the best approach I've found so far. Hopefully Prusa will add something more streamlined in the future. In the meantime, this works for me.

RE: How to change default settings for all profiles?

You can easily make any changes in all your profile files at once with Notepad++. See the picture. Replace [--] with your username. If your settings are stored in another directory, change the whole path accordingly.