Extracting pack.idx/dat is quite simple indeed!
1) Use a text editor ( for me, I use the Ultra Editor) to open the pack.idx file and open RTW's animation\pack.idx file, too
2) Replace the first 16 bytes of the M2TW's pack.idx with RTW's(See pictures)
3) Use the Vercingetorix's IDX extractor to extract them!!
4)mod, but I don't know how
5)Pack them using Vercingetorix's IDX. If you want them to work you have to replace the first 16 bytes with your original M2TW's pack.dat & pack.idx's
For those who want to extract skeleton.idx & skeleton.dat:
It appears that we can easily use Vercingetorix's IDX extractor to do this job. BUT, in fact, there will be something wrong! If you do so you can check the file list. Then you will find that one file is MISSING! that is "MTW2_Halberd_Primary". Actually there'er TWO "MTW2_Halberd_Primary" files but we are able to extract only one of them.
So, Here is the relatively correct step:
1) open skeleton.idx, again using UltraEdit. Find the string "MTW2_Halberd_Primary". There will be two. Edit one of them to, for example, "MTW2_Halberd_Primara".
2)Extract them using Vercingetorix's IDX extractor.
3)mod, but I don't know how
4)Pack them using Vercingetorix's IDX extractor.
5) Open your repacked skeleton.idx/dat, repalce the first 16 bytes with the original M2TW's. And don't forget to find the string "MTW2_Halberd_Primara" in your repacked skeleton.idx and change it back to "MTW2_Halberd_Primary".