I wanted to use mesh from a store outfit and make the top part of it into a top. Am I allowed?

That's an interesting question, I'm working on bringing it to the attention of someone who can give you a definitive answer

Why not? Other people have.

I'd be interested in the definitive answer to this too. I was under the impression that because Store files are packaged in a 'Protected' format that can't be opened without first using a hacking tool to remove the protection, that modifying and redistributing them was not legally allowed.

For an example, on this site, I remember that a while back there was a series of edited Store hair uploads that contained both the meshes and textures so that purchasing the original hair was not necessary, but then policy was changed to only allow uploads of the edited mesh without the textures included, so that the player would need to buy the original Store hair to link the textures with. But recently, there have again been uploads of edited Store hairs that contain both mesh and texture. So I'd be really grateful to know the exact policy on this, because there are a few Store items I'd like to use as a base for new creations myself! It would be really handy if we're allowed to do so.

I'm not keen on the idea of publicly sharing such stuff on a high profile site. I don't think any of us will be better off if EA react by making their encryption harder to deal with. At least when done discretely we can still sort of get into those files.

Yes, my thoughts exactly. I would not want MTS to incur the wrath of EA if these items are deliberately designed to not be opened. Of course if someone is just using it for their own personal game and not sharing it, that's one thing, but redistributing it does seem like it would be a no-no.

Using s3rc is not, itself, against MTS rules - it can be used for legitimate purposes on both legitimate and illegitimate store files, just like any other modding tool. We have, in the past, not allowed any unmodified resources from Store content to be included in uploads - in the case of those hairs Esme mentioned, they were mesh edits which didn't alter the textures, so we required that the textures be repo'd to the original store files. We've stepped back from that policy a little now, though; the present rule is that an upload shouldn't effectively redistribute a Store item in its original form (or with tiny/insignificant changes). Using Store meshes and textures (and other bits) as bases for an edited item is totally fine.