This UDF overwrites the blending function in regions where x2:

  #include "udf.h"
  DEFINE_KW_GEKO_BF(user_geko_bf, c, t)
   {
      real bf_value;
      real xc[ND_ND];
      C_CENTROID(xc,c,t);
      if (xc[0]>--> 2.0)
        bf_value = Get_Geko_Blending_Function (c, t,
                   C_R(c,t), C_MU_L(c,t), C_WALL_DIST(c,t),
                   C_K(c,t), C_O(c,t));
      else
        bf_value = 1.0;
      return bf_value;
   }