You can change the default excess of reactants manually by the --ratio (-X) option.
react -r da.mrv "C=CC=C" "C=C" -X 1:1
react -r da.mrv "C=CC=C" "C=C" -X 2:1
react -r da.mrv "C=CC=C" "C=C" -X 3:1
Note: Results are written to the console.
Ratio: Reactant ratio is considered as the number of cycles of the reaction. Zero (0) means an infinite number of cycles. This consideration is also feasible when only one reagent can be set in a reaction. For example, a reaction on a primary amine group will be repeated until all hydrogens are substituted if the ratio coefficient is 0 and will be stopped at a secondary amine if the coefficient is 1.