This paper presents genEPJ, an open-source Python library that automates the implementation and optimization of EnergyPlus models using IDF, epJSON, eppy, OpenStudio, and Modelkit templates. With more than 100 preconfigured functions for modifying EnergyPlus input files, genEPJ streamlines the creation of reference, proposed, and optimal designs for building configuration analysis and parametric or optimization studies. The library helps practitioners prioritize model consistency instead of manual modelling tasks while supporting innovative workflows. It also enables resilience analysis by simulating building performance during outage events and supports multi-objective optimization for energy efficiency, cost-effectiveness, resilience, and annual and hourly emissions performance indicators overall.