By default new skins will load at the top left corner of your monitor (unless specified within the skin). It would nice if I could use DefaultWindowX, DefaultWindowY, DefaultAlwaysOnTop, DefaultSnapEdges etc within the [Rainmeter] Settings.ini
This would give me a way to specify exactly where all new skins appear.
My current setup is 3x 32" 1440p, with the primary being the center monitor but all new skins load on the top left corner of the left monitor.
There is no way to do that globally for all new skins that are loaded, and to be honest I'm not sure I see a sufficient use-case for that, but you can set defaults for individual skins.
You set these default values in the [Rainmeter] section of your skin, and then the first time it is loaded by anyone, it will initially use those values.
There is nothing "global" that will do that in Rainmeter.ini. As I said, I just don't see an important case for that. You may want all new skins to load centered or something, but you are likely one of the few people in the world that would want that. I mean, why would I want every skin I load using Manage to appear behind the Manage dialog, where I can't easily get at it? The current behavior is fine for almost everyone, as it is certain and predictable.
A possible alternative would be to use an "always loaded" skin for this purpose, that would parse Rainmeter.ini using WebParser, use the !WriteKeyValue bang to write the desired coordinates for every skin having a section in the file, and then use a !RefreshApp bang to reflect those changes visually, all of this on a mouse click or something like that.
That being said, I'm not sure how feasible or comfortable this would be, how many "side problems" it would create, or if it would worth the effort...