You're all good man, those are legit questions.
You can lengthen the port or shorten it to change tuning. How this change is done matters; if the port is made longer and the port is all internal, then you can lose airspace, which changes literally everything. So, say you made an aero port longer inside of a box, then you'd want to calculate everything that changes, all together at once
Changing the port area can greatly affect how a system plays. I use port area sizes to manipulate how the box plays, you can control impedance changes, somewhat, when you understand the relationship of port sizes, box net airspace, and port tuning. You can purposefully limit a sub's movement with combinations of previous mentioned factors, and that can really help with voltages, overall system stability and bandwidth. It's all box by box dependent. It's all custom to the user and their system.
Sometimes I adjust box sizes based off wanted tuning. Sometimes subs like a certain box size, regardless of tuning, to whatever extent. In short, yes, you can change the sound of any box by modifying the port. In larger bandpasses, such as walls and blow throughs, I try to leave or fundamentally integrate the option of potential port changes, especially in series 6th orders.
I've done ported boxes that have very long removable ports, so a 40-45 hz port could be put in for SPL. You literally just unbolt the port and pull out a daily skinnier port that's like 30" long or so, and drop in a port that's shorter with a huge port area, for SPL burping. If the layout and space allows, I can design enclosures with adjustable or replaceable ports, I do it somewhat regularly.
