This should do it. Select your compositions in the project panel and run this. Replace [100,200] on row 13 with what values you need
function changeParagraphSize(myComp,newSize) {
for (var i = 1; i <= myComp.numLayers; i++) {
var crtLayer = myComp.layer(i);
var t = crtLayer("ADBE Text Properties")("ADBE Text Document");
var td = t.value;
td.boxTextSize = newSize;
t.setValue(td);
}
}
function changeParagraphSizeInProject(){
var comps = app.project.selection;
for(var i=0; i<comps.length; i++){
changeParagraphSize(comps[i],[100,200])
}
}
changeParagraphSizeInProject();