The problem with your mod not starting up is almost certainly with the MODELDB file. I hope you backed that up before modding it otherwise just reinstall the mod.
Open up the MODELDB file and click on edit in the toolbar at the top, then select find. Type in 10 musketeers, this will take you straight to where we are going to add musketeers in for Sicily. We will copy the Portgual model because it is the closest colour.
10 musketeers
1
4
54 unit_models/_Units/RN_Light_Lmail/musketeers_lod0.mesh 121
54 unit_models/_Units/RN_Light_Lmail/musketeers_lod1.mesh 900
54 unit_models/_Units/RN_Light_Lmail/musketeers_lod2.mesh 2500
54 unit_models/_Units/RN_Light_Lmail/musketeers_lod3.mesh 6400
6
5 spain
71 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_spain.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
40 unit_sprites/spain_Musketeers_sprite.spr
8 portugal
74 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_portugal.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
43 unit_sprites/portugal_Musketeers_sprite.spr
5 milan
71 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_milan.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
40 unit_sprites/milan_Musketeers_sprite.spr
6 venice
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_venice.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
41 unit_sprites/venice_Musketeers_sprite.spr
6 france
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_france.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
40 unit_sprites/spain_Musketeers_sprite.spr
7 england
73 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_england.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
42 unit_sprites/england_Musketeers_sprite.spr
6
5 spain
67 unit_models/AttachmentSets/Final European CB Gun_spain_diff.texture
67 unit_models/AttachmentSets/Final European CB Gun_spain_norm.texture
0
8 portugal
70 unit_models/AttachmentSets/Final European CB Gun_portugal_diff.texture
70 unit_models/AttachmentSets/Final European CB Gun_portugal_norm.texture
0
5 milan
67 unit_models/AttachmentSets/Final European CB Gun_milan_diff.texture
67 unit_models/AttachmentSets/Final European CB Gun_milan_norm.texture
0
6 venice
68 unit_models/AttachmentSets/Final European CB Gun_venice_diff.texture
68 unit_models/AttachmentSets/Final European CB Gun_venice_norm.texture
0
6 france
68 unit_models/AttachmentSets/Final European CB Gun_france_diff.texture
68 unit_models/AttachmentSets/Final European CB Gun_france_norm.texture
0
7 england
69 unit_models/AttachmentSets/Final European CB Gun_england_diff.texture
69 unit_models/AttachmentSets/Final European CB Gun_england_norm.texture 0
1
4 None
16 MTW2_Fast_Musket
20 MTW2_Non_Shield_Fast
1
19 MTW2_Musket_Primary
1
18 MTW2_Sword_Primary
16 -0.090000004 0 0 -0.34999999 0.80000001 0.60000002
Above 5 spain look at the number 6 delete it and type 7 then you must leave 1 space after it on the same line. Further down their is another 6 above 5 spain, change that to a 7 as well. We will now add Sicily to this unit model. Copy the text in red below england:
7 england
73 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_england.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
42 unit_sprites/england_Musketeers_sprite.spr
6 sicily
74 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_portugal.texture
72 unit_models/_Units/RN_Light_Lmail/textures/RN_Light_Lmail_normal.texture
43 unit_sprites/portugal_Musketeers_sprite.spr
There must be 1 space left after each line or it wont work. Then add this in red below:
7 england
69 unit_models/AttachmentSets/Final European CB Gun_england_diff.texture
69 unit_models/AttachmentSets/Final European CB Gun_england_norm.texture
0
6 sicily
70 unit_models/AttachmentSets/Final European CB Gun_portugal_diff.texture
70 unit_models/AttachmentSets/Final European CB Gun_portugal_norm.texture
0
Note that there must be 2 spaces after the 0 here, save and exit. You should now have musteteers for Sicily working with textures