Hi 'Rotney'
I had to get an interim EAD from the Dallas office in March of last year. The first thing I would advise is to get there early. I ended up going twice (see below), and on the first occasion didn't turn up until about 5am, which meant that I didn't get seen until about midday. The second time, I arrived at 4am and got seen by about 8am. I certainly wouldn't recommend going any later than 6am otherwise I don't think you will get in. Also, be aware that they are closed on Wednesdays.
The first time I attended for the iEAD was on the 91st day after the RD, and about four days before my current EAD expired. After the long wait I was turned away since they said that they cannot issue an iEAD until the existing EAD has expired. I later discovered this is completely wrong, and there is a memo from the director of TSC to the local offices (I have a copy somewhere) requesting that they issue iEADs after 90 days. However, when the officer says 'no', there is very little you can do to argue the case. Therefore, I had to go back once the EAD had actually expired.
As regards interim APs, I don't believe there is such a thing. I think in genuine emergencies the local office can issue an AP which is essentially the same as that provided by the service centre. Luckily, I've always had the AP renewed in time, so I have no direct experience of this. However, I will say that when I went to the Dallas office just before Christmas for passport stamping (finally approved
), there was a lady in line immediately in front of me who was trying to get AP to go and visit her sick brother and she was turned away at the initial screening window since although she had a doctors letter, it didn't actually state that he was dying. Therefore, it looks like you need a really serious reason to stand any chance of getting AP from the Dallas office.