There may be a better way of doing this, but...
Load the shaft, anus and material copy as normal.
In "Materials v2" using the shell selector, apply the preset that you want. The body now turns the flesh colour.
In the scene tab, select the "Male Centaur Body" and go to surfaces tab. Find "1Coat" and change the base colour to "01_CentaurMaxxCoat_D".
You'll now see the gens and anus are textured, but the coat texture's still missing.
In scene tab, select the "easy rider shaft", go to surfaces tab and select "coat" - change the base colour texture to "01_CentaurMaxxCoat_D" and the colour should be all 1.00.
Repeat for the anus and the girl bits, if they're there.
Finally, in the scene tab, reselect Centaur Maxx HD and reload his "Centaur Maxx !All Mats Complete" material - this retextures the whole figure and will fix the transition between horse and human.
Good luck! Thunderstorm's about to hit here, so I may be off for a while.
How much can a Koala bear?