In the beginning of the runf-file, write:
##
## Keyword to force gensys to update the massmatrix in every time step
## -------------------------------------------------------------------
update_mass_matrix
In the end of the runf-file, write:
##
## Update the track masses
## -------------------------------------------------------------------
func update_mass trc_111r zz mztw_111r
func update_mass trc_111l zz mztw_111l
func update_mass trc_112r zz mztw_112r
func update_mass trc_112l zz mztw_112l
func update_mass trc_121r zz mztw_121r
func update_mass trc_121l zz mztw_121l
func update_mass trc_122r zz mztw_122r
func update_mass trc_122l zz mztw_122l