When performing a superstructure replacement, it is common to design the proposed superstructure in LRFD but then analyze the existing substructure capacity in LFD. Currently with LEAP Steel, because the superstructure was designed in LRFD the substructure analysis/design module forces you to analyze the substructure in LRFD. If you allow the change to LFD within the substructure module (the drop down is there, it's just grayed out and defaulted to the same as the superstructure design) it would make analyzing this type of rehab project much easier.