Copy CustomXHair.utx to the Textures folder.

Open User.ini.
Find section:
[Botpack.ChallengeHUD]

Replace the following lines:
CrosshairCount=18
CrossHairs[0]=Botpack.CHair1
CrossHairs[1]=Botpack.CHair2
CrossHairs[2]=Botpack.CHair3
CrossHairs[3]=Botpack.CHair4
CrossHairs[4]=Botpack.CHair5
CrossHairs[5]=Botpack.CHair6
CrossHairs[6]=Botpack.CHair7
CrossHairs[7]=Botpack.CHair8
CrossHairs[8]=Botpack.CHair9
CrossHairs[9]=CustomXHair.2x2
CrossHairs[10]=CustomXHair.4x4
CrossHairs[11]=CustomXHair.4x4Soft
CrossHairs[12]=CustomXHair.CHair6
CrossHairs[13]=CustomXHair.CHair7
CrossHairs[14]=CustomXHair.CrossEmpty
CrossHairs[15]=CustomXHair.ThinCross
CrossHairs[16]=CustomXHair.ThinCrossEmpty
CrossHairs[17]=CustomXHair.X
CrossHairs[18]=
CrossHairs[19]=

The Botpack crosshairs are the default ones.