Well, this is quite an interesting thread. So basically, I can use ACF on my multisite to:
1. create a custom theme with a custom field, let’s say “site-icon”. Within the theme, get the value of the “site-icon” and display it, e.g. “fa fa-wrench”.
2. activate that theme on some of my subsites
3. choose a value for each “site-icon” in each subsite (“fa fa-wrench”, “fa fa-globe”, …)
ACF will then show each individual “site-icon” for each subsite?
That would be exactly what I need !! But does it work this way?