We might want to keep in mind this concept: Programs in Flynn's grid "power" things that are "attached" to them, or synchronized to them. This includes their disc, if they have one. But also, personal vehicles that can be compressed and re-rezzed, such as light cycles and light jets. Essentially, when a program takes possession of anything, it seems the rules are that it becomes attached to them - there's a system call or link established between the program and the extra data.

This might make ultimate sense of the variety we see in Legacy, as long as we're rationalizing things. For example, Quorra's sleeves can be pulled down; it's not like she is a simple character model and her costume is part of her. however, note that when her arm is cut and derezzes, part of her sleeve is derezzed with it. And when she is repaired, and her arm re-rezzes, her sleeve also begins to re-rezz.

Basically, this is because when Quorra has her Grid Warrior uniform on, it is synched to her, personally, and also shares her fate - including damage to code.

Thus, in the case of programs (or "basics") in general, I think it's fair to assume they can change uniforms and clothing if they wish. Remember that Castor stalled Sam by mentioning they'd have to "get him a change of clothes"! However, unlike in the real world, clothing articles in the Grid, whether made to look like loose fabric, or form-fitting kevlar or latex, don't get dirty and need to be washed or ever taken off for maintenance purposes. So a program may spend fifty cycles if they wish, wearing one particular costume, then choose to change it, or have it changed to something new. If a program is say, damaged while they're wearing a piece of clothing, it will be derezzed too. But as seen with Sam getting the cloak from the "bum", the items can simply be handed over and change ownership/linking.

As for what else is under a program's clothing, ah-heh. Well, given that programs are made to look really authentic to the eyes of a User, and that they drink liquid power, and in Quorra's case, can *eat* food made to work like human food, I imagine it this way:

ISOs, Programs, and Basics, do not bleed when cut, and when partially derezzed, display a clearly artificial "digital" interior. But the damaged sections we see are merely blocks of data (literally blocks!) where their simulation has crashed! When a program is running correctly, I think they have some simulated internals and human components. They're not simply solid inside. They may even have a "low resolution" simulation of the human body inside - everything might look as if it was an anatomical model molded out of soft plastic or clay.