Well I still remember how I managed to make the transition succesfully from the non-aspect wind serpent to a flaming horse, if by any chance anyone is still interested.
What you need first:
1. Make a copy of each of the following files: creatures.txt, itemtype.txt, creatureinfo.txt, soundprofile.txt and blueprint.txt (this one will not get modified, will only be used as a reference, but hey a copy of it cannot hurt).
2. I recommend not using Windows incorporated text editors for the following alteration (the files are kinda huge for some texts); I used Notepad++ and it worked like a charm.
Ok then, the steps are as follows:
1. First find the id and itemtype_id for the mounts you are insterested in. Each mount has their own id and itemtype_id. The best way of finding these is by searching with "specialmountfor = X" in the creatureinfo.txt, where X would be the class that the unique mount corresponds to. (so far I know that dryad is 2, high elf is 5 and seraphim is 1; ALSO the non-unique mounts are a bit more difficult to find since they have no "specialmountfor = X" tag describing them, which means that it would be better to search for them in the creatures.txt file since there they have a name tag, although the names are not very suggestive but they help a little).
-- btw the itemtype_id for the flame horse is 12736, for the non-aspect wind serpent is 5549; you can search on google for these itemtype_ids as well - you might get lucky;
2. Go into the itemtype.txt file, search for the itemtype_id of the mount from which you want to copy the 3D model from (in my case it was the flaming horse) and COPY the 3d model section (that means everything from "-- 3d model" line to just above the "-- logic bounding box" line); now search for the itemtype_id of the mount that you want overwritten (in my case it was the non-aspect wind serpent) and paste what you just copied over the same area of the target mount (it does not matter if the number of lines is different, as long as you overwrite the entire 3d model section).
-- right now the 3d model is changed, and if you try to run the game at this moment you might get a very weird mount instead of the one you got, or you might just get something usable - anyway it is not done yet).
3. Go into the creatureinfo.txt file. Search for the itemtype_id of the source mount (for me the flame horse) and copy everything from just below the "type = number," line down to "} mgr.creatureInfoCreate(newCreatureInfo);". Now search for the itemtype_id (just to be sure I'm reffering to the number you first found at step 1, not the string "itemtype_id") and here paste over the area of the target mount (in my case the wind serpent.
(Please NOTE that the "specialmountfor = X," line is essential and thus should not be copied over, or to be more precise it needs to survive your pasting attempt; also if a line that looks like this " eq_fallback = { number }," survives your animation during game will be messed up, which also means that if you want to paste over a unique mount - whereas the flaming horse is a normal mount - you will need to copy the " eq_fallback = { number }," line from the source mount)
-- now you might wander why the NOTE is important (and btw it is in most cases); well it is because only now will your animation work properly (for instance your flaming horse will not have a tail if you fail at this step - tailItemtype is not 0 in his case)
4. This one is OPTIONAL. At an earlier reply the attribute parts of your mount are mentioned. The "mgr.addCreatureBonus" and the rest of the attributes are correctly mentioned. Now let's see what those things mean. First of all at this point you have to use the id that you found at step 1 rather than the itemtype_id. How to use this id is explained by Malachor. So let's see the meaning behind the code presented there. The first three blocks (out of 6) refer to the positive bonuses that you get from that mount; to be more precise the first block refers to the resistance/aspect cooldown reduction that you get from you mount. The second refers to the health bonus, and the third to the defense bonus (they are described ingame in the same order that they are presnt in the creatures.txt file). Now how can you find out what they really are about? Well in that block you have two variables: intensity and bonus. Increasing and decreasing the intensity will make that bonus greater or loewr. The bonus variable is mapped in the blueprint.txt file. You can search for it with a string similar to this one: "createBonus(number", where number is the number that the bonus is equal to (in the case of the first block it would be "createBonus(248"). By searching this way you can find out what the added attribute means.
Now regarding the 4th and 5th block, well I still don't know their exact purpose but I saw no difference wheter I left the code there or if I just deleted it.
NOTE that the +54% in all aspect cooldown cannot be removed from this place. It seems to be directly linked to mount itself, and even if you will delete all attributes of the mount in the creatures.txt no description will be available but the increase in cooldown will still be applied.
As for the last block, from what I could gather it is linked to what you see in your inventory. I did not bother to alter it but if anyone is curios he/she can try and perhaps give some feedback.
5. This is also OPTIONAL. At this point some of you will probably still be bothered by the sounds your mount makes. The animation was changed but the sound is still the old one. So in order to change this go into the soundprofile.txt file, search for the itemtype_id of the source mount (the line should look something like "typex = itemtype_id" ) and replace it with the itemtype_id of the target mount. Then swap the itemtype_id of the target mount from the place where it is originally put with the itemtype_id of the source mount (basically now the non-aspect wind serpent makes horse sounds and the flame horse that you can buy under normal circumstances makes wind serpent sounds). If you are wondering why I did not use a more professional method, well I tried, but it seems that adding new line or comment others can results in a total loss of sound ingame, so be careful).
Guess this is just about it. By the way I tried this on CM 0130. Hope it works for you.
