To change moderator density from 1.1929 g.cm^3:

! Moderator D2O
! Atom purity - 99.91 %
! Density 1.0829 - g/cm3
! Temperature - 346 K

! COMPUTE DENSITY AND WGT% FOR MODERATOR          
INFO: ::              TMP: <<Tmod>> K 
                      PUR: <<Pmod>> ATM% 
                      CALC DENS WATER >>Dmod<<
                      LIB: WIMSD4 FIL: IAEALB
                      ISO: 3 <<nam1H>> <<nam2D>> <<O16>>
                      CALC WGT% D2O >>wgt1Hm<< >>wgt2Dm<< >>wgtOXm<< ;

[Add the following lines:]

Evaluate Dmod := Dmod 0.9 * (or other value of factor)