This is an edited cockpit livery, but also a mod.
Cockpits can have liveries just like the external model of an aircraft. However it's not as popular, and for most modules comes with only a few versions, such as "Native", "English", "Russian" or "Chinese”
I cannot create a separate livery for the cockpit, as for whatever reason DCS will not see or acknowledge it. It only will if the modded cockpit livery is named "default." Thus, this mod cannot be added along side the default cockpit livery, it must be overwritten. I'd suggest taking the "default" cockpit and backing it up or something first.
The most important change this mod does is remove the smudges on the inside of the canopy glass
-Canopy reflection texture is reduced towards the back
-Real canopy reflections are smoothed
-Cockpit photo added, as a bonus. You can change it if you want. Note however, that if you do, stretch it horizontally by 145%, due to how DCS will scale it.
1) Navigate to DCS World.../Mods/aircraft/P-51D/Liveries/Cockpit_P-51D-25-NA
2) Rename your unedited default cockpit livery to something easy such as "default [original]"
3) Drop in the modded "default" cockpit livery into the Cockpit_P-51D folder
4) Back out to the Liveries folder, and do the above steps to the P-51D-30 (Cockpit_P-51D-30-NA)
Photo included as well, to remind you (or myself at this time) how to properly sight a target with the K-14