In the battle data loading routine, 08028B56 mov #0x14 into r0, moves the offset for strength in the battle data into r0, and 08028B58 ldsb r0, [r5, r0], loads the value of strength into r0. The subsequent line adds it to the ongoing calculation of might. To change it to skill, for example, just change 08028B56 to mov #0x15 instead.
(This doc probably won’t be necessary once I finish my modular battle, but hey, docs on vanilla FE7 are good, right?) (Nintenlord’s docs have the whole unit structutre, and probably this documented there somewhere(he did load magic at one point, right?), but this is a specific description that I think will still benefit people, especially those searching through these forums for documentation.)