I hear you—you're trying to change what the pins display on the symbol.
This is the most relevant entry I found related to pin configuration. Quote (verbatim):
"Symbol Configuration
These properties configure how the pins will be aligned with the symbol. Remember that you need to publish the part to the library and place it on a project in order to see its symbol.
Property: Pin Number
Applicable to: Terminals
Use case: Defines the pin number of said terminal. The assigned pin number will be assigned in the PCB editor as well.
Property: Pin Orientation
Applicable to: Terminals
Use case: Defines the pin orientation in the symbol. For example Pin Orientation = left locates the target pin on the left side of the symbol, Pin Orientation = right locates the target pin on the right side of the symbol,
Property: Pin Group
Applicable to: Terminals
Use case: Terminals with the same Pin Group property will be grouped closer together in the symbol. If a terminal's Pin Group property is left empty, they will not be grouped in the final symbol, and will have a larger gap between them.
Property: Section
Applicable to: Terminals
Use case: Terminals with the same Section property will be located in a specific section in the symbol, labeled the same as the Section property. If a part has multiple sections, each will be labeled accordingly and they will be separated with horizontal dividers.
Property: Terminal Order
Applicable to: Terminals in parts with default symbol
Use case: Defines the pin position in the default symbol. For example, in a 4 pin symbol, Terminal Order = 1 is the top left pin in the symbol, Terminal Order = 2 is the bottom left pin, Terminal Order = 3 is the top right pin and Terminal Order = 4 is the bottom right pin.
Property: Symbol Pin Position
Applicable to: Terminals in parts with custom symbol
Use case: Defines the position of the pin in a custom symbol. To learn more about how to configure a custom symbol, check out this tutorial#2--creating-a-symbol
Property: Sub-symbol Designator Suffix
Applicable to: Terminals in parts with parametric symbols
Use case: Splits the symbol into multiple parts, each with its own suffix To learn more about how to configure a multi-part symbol, check out this tutorial.
#multi-part-symbols"
I couldn’t find documentation for a “pin name” field that would show labels like GND/3V3 on the symbol pins themselves. That probably means it isn’t currently supported. If you want to push on this, the best next step is to ask in the Flux community so the team can advise or log it as a feature request: