[Vpmedia]

you need to edit the *.DB files in the Dgen folder

for example:

C:\Program Files\Ubisoft\IL-2 Sturmovik 1946\DGen\Africa40.db

...
[Planes]
34 CR_42 insert *.bmp here
4 JU_52_3MG4E vp_desert_campaign.bmp
2 C_47
4 BLENHEIM4 blenheim_Singapore.bmp
18 GLADIATOR1 Spain1.bmp
10 GLADIATOR2 Spain1.bmp
1 U_2VS U2trop.bmp
[Skill]
...

if winter available in that campaign (Stalingrad for example) you can add to bmp's

2 C_47 summer.bmp winter.bmp