Landing gear is for sissies!
The Except.DAT file is based on Filelist.DAT and is a "pointer" file.
This is a sample from the file, using HexWorkshop:

The purpose of Except.DAT is to tell RB2 to use other texture bitmaps for those which are missing. It also reduces the number of files needed. There is no point in having 18 identical wheel files, for example.

If you have not already studied the Filelist page, then do so before continuing.

In the "header" we have one VERY important bit of information. The number of records in the file. If this value is not changed as you go along, the bitmaps at the end of the file will be ignored. We will look at how this header works: 0911 0800 0200. Starting with 0911, this is the Number of Records in the file (1109). 0800 is the record length in bytes (8), and 0200 is variables per record (2). In Filelist.DAT this value is 1 and in Except.DAT it is 2 (one bitmap being replaced by another). To arrive at the number of records after you are done adding bitmap names, you have to do the following:
1. Put the cursor right after the last digit in the file ( - at the very end of the file).
2. Note the offset number at the bottom of your screen.
3. Bring up a HexCalculator under Tools, and enter this number. (trying to figure it out via decimal system is a veritable pain).
4. Subract 64 (Hex) from this number. You will notice that the first Fokker bitmap reference starts at 000064
5. Divide by record length, in this case 8.
6. Enter the result, but with the low and high bytes switched. In the above case the calculator result would show 1109, but you enter 0911 into the file.

Now for the bitmap names:

I have highlighted 5 segments:

The first, in purple, is telling RB2 to use the fuselage of Jasta 10 for Jasta 12. How?
1200 0003 is the Fuselage for Jasta 12, 03000012. It is being replaced by 1000 0003 or 03000010, which is the fuselage for Jasta 10.

Just above the pink box is a reference for the default fuselage bitmap used by squadrons which have no schemes defined. Fly Now, for example.

The pink box is highlighting the replacement of the Upper wing texture of Jasta 14 to that of Jasta 10.

The green box highlights a convenient feature. Here, RB2 is told to use the upper surface texture of the elevator for Jasta 10 on the bottom surface as well. Note that Both 4-byte segments start with 0x10.

The red box is similar to the former one, but here Jasta 5 Elevator bottom is replaced by Jasta 10 Elevator top.

The red series of numbers at the bottom is the first replacement pointer for the Aviatik C.I, FA 2 to FA 1.