LEAP does allow users to specify an emissions constraint under the high level "Effects" branch (located between Key Assumptions and Demands), but the constraint is applied to the whole energy system, not a specific module (or power plant). This constraint is used in the optimization calculation to determine the least-cost configuration of a module. For more information, take a look at the following web page:
https://www.energycommunity.org/Help/Transformation/Emission_Constraint.htm