Warhawk. You can edit the API yourself in Notepad (or the Edit Macro feature in your scenery design program). Simply change the file name of the approriate texture to the one you wish to use.

For example:

; BGL_TEXTURE: tclass=1h color=79EF7979 name=people9.bmp
Dwx( 0043 0018 0000 0001 ef79 7979 )
Dba(people9.bmp)    
Dbx( 00 )
Smoothing( 1 )
Inst_7d
TexPoly( 0 0 -32767 0.00  0 0 1 1 0 255 2 126 255 3 126 1 )
Inst_7d
TexPoly( 0 0 32767 0.00  7 0 0 6 0 255 5 127 255 4 127 0 )
Poly( 0 0 0 0.00   5   1   0   4   )
Poly( 0 0 0 0.00   2   6   7   3   )
Poly( 0 0 0 0.00   5   6   2   1   )
Poly( 0 0 0 0.00   0   3   7   4   )
Smoothing( 0 )
Return

I assume you're modifying an existing macro. Without knowing the particular macro I can't say if it uses more than one texture. Providing you keep to the original texture configuration edit the file names accordingly in the API. There will most likely be more than one texture entry.

If you care to zip up the complete thing including your modified textures & mail it I'll be happy to check it out for you. My E-mail is under my avatar or in my profile.