Yes. I only know how to do the stuff you see when you pick your own person, and I haven't done much in this area, but here is a start:
(Updating this is a front end action, rather than a in-game action, when you are in modbuddy.)
If you update the table Players, each playable combination of CivilizationType LeaderType combo has a row. There are a few relevant columns:
LeaderIcon
LeaderAbilityIcon
Portrait
PortraitBackground
Most portraits are left as Null in this table, presumably the game knows to autofill, but you can assign it and get results.
There's LEADER_ELEANOR_FRANCE and LEADER_ELEANOR_ENGLAND, and their leader icon and leader ability icons are ICON_LEADER_ELEANOR_FRANCE etc. Their portraits for the civ select screen are LEADER_ELEANOR_FRANCE_NEUTRAL and LEADER_ELEANOR_ENGLAND_NEUTRAL. I don't know about the PortraitBackground, though.
You can search these forums for how people do the in game stuff (when you meet an AI etc) and it's almost certainly just a matter of swapping _ENGLAND and _FRANCE where you need it. This goes beyond my current understanding, though.
