Can I mix profiles from different standards (IS + AISC) in the same project?

Yes, and CalcSteel supports this natively — you can have ISMB beams, W-shape columns and SHS bracing in the same 3D model. The catalog contains 1,140+ profiles from AISC, Eurocode, NBR, IS, AS and more. For verification, however, you should pick one governing design code per check. Mixing IS 800 profiles verified with AISC 360 formulas is technically possible but creates traceability problems in your calculation report. The best practice: use the profile catalog freely, but set your analysis standard based on where the project will be built and what the local authority requires.