I only know about this:
defaults write com.apple.finder DesktopViewOptions -dict IconSize -integer 188x188px.; killall Finder’
But it’s only for the Desktop…
Open a Finder window in Icon mode (⌘1), then click Show View Options (in the View menu, or ⌘J). Make the changes you want, then click the Use as Defaults button at the bottom of the panel to make it stick for all folders.
How about Finder > View > Show View Options > Icon Size?
(I'm not 100% sure about the naming as I don't have a Mac currently with me...)