You can specify in Equation 8.6-1 on a per-scalar basis, directly, through user-defined functions (UDFs).
To specify a UDF for anisotropic diffusivity on a per-scalar basis, first select a scalar equation (e.g., uds-0) from the User-Defined Scalar Diffusion list in the UDS Diffusion Coefficients panel (Figure 8.6.7).
Then choose user-defined-anisotropic in the drop-down list under Coefficient. The User-Defined Functions panel will open allowing you to hook a DEFINE_ANISOTROPIC_DIFFUSIVITY UDF only if you have previously loaded a compiled UDF library or interpreted a UDF. Otherwise, you will get an error message.
Refer to the separate UDF Manual for details on user-defined functions.