I haven't tried it, but as long as they have the same window node, that should be possible. If you are having an issue, it might be with the target[1]. I had several issues dealing with that. You can avoid that by using database handlers instead.
For example.
<template name="number_charabilitychareaction">
<number_abilitybonus>
<anchored position="righthigh" offset="15,0" width="36" height="20" />
<hideonvalue value="0" />
<modifiersize>mini</modifiersize>
<script>
function onSourceUpdate()
local nodeWin = window.getDatabaseNode();
local nCurrentScore = DB.getValue(nodeWin, "abilities.charisma.score", 0);
nReaction = GameSystem.getAbilityChaReaction(nCurrentScore) + calculateSources();
setValue(nodeWin, "abilities.chareaction.bonus", "number", nReaction);
end
function onInit()
local nodeWin = window.getDatabaseNode();
DB.addHandler(DB.getPath(nodeWin, "abilities.charisma.score"), "onUpdate", onSourceUpdate);
super.onInit();
end
</script>
</number_abilitybonus>
</template>
On init, set up database handler to watch the charisma score.
On source update of the charisma score, find the value of the charisma reaction bonus based on the new charisma score.
Set the value of the charisma reaction bonus.
This avoids the use of target[1] and will likely avoid lots of problems because of it, and as Trenloe said the other day, is best to directly work against the database.
Should be no reason using this technique that you can't do two setValue's at once, that I'm aware of.