[lowfighter]

In a hurry but it's like this

In load.ini the random trees textures are given by the Tree0 for example:
Tree0 = Trees\AlteredBush8a.tga
If you extract with sfsextractor maps.sfs you get in maps/_tex/trees/ the following textures
AlteredBush8a.tga
AlteredBush8aTL.tga
AlteredBush8aTrunkTL.tga

Create your own which should have the name format

bla.tga
blaTL.tga
blaTrunkTL.tga

place them in something like

mods/mapmods/maps/_tex/trees/redko/

change the line in load.ini to

Tree0 = Trees/redko/bla.tga

Note that all 3 files are required.

It's not gonna affect any other map than yours.

You can find such tree new textures to download: AAA search Rus_Andrey trees for example
Also Neil_Lowe's Darvin map has his own custom trees.