You can select that in the interface, sell or store, it's the same for all modules and it should be because that way it's not confusing, having that option for some modules and not others would be strange, and make for more complex code, and the more complex code you have the more likely there are to be bugs. The KISS principal applies, don't make stuff more complex than it needs to be.
Sorry I don't quite understand YOU, if I'm at a station and I want to buy a core module I have a choice at the bottom right to put that module in stock or sell it immediately.
They even warn me about it in red. But why don't I have such a choice when replacing a module ?
Is this a KISS ?
P.S. After re-equipping my ship I have to sit and click 10 times to sell all my E modules from stock. Must be KISS.
Because you can replace any module in your ship with one you have in storage at that location even if it is a module the station itself doesn’t sell, if they don’t sell them why would they buy yours?
Why doesn't it sell? The price is very much taken into account. Even on aircraft carriers, these modules magically appear on the ship out of thin air for money.