Altium: How to change designator font when creating new library?
It's a bit tricky, but for single parts/components you can do that. You have to be in the SCH Library. Just go to "SCH List" in the panels.



A new Window should open. You have to change the mode from "View" to "Edit" and change the objects to "non-masked objects" at the top-left corner.



Afterwards, you can change every font, size and color of every parameter. For designators you just scoll down to "Designator" and in the "Properties"-panel the Font, Size and Color might be changed.



If you want to change all Fonts, just select "all components" and include only "Designators".



But I would NOT recommend doing it. Because if you add another component to you lib, you have to think about this process and change it every time. Same goes for parts and components that are from third-party.