Should be fairly simple, though I haven’t seen your document. Prepare your document as follows: on each master page place a text frame for the page number and name it ‘folio’ (without the quotes) on the Layers panel. Then run this script:
(function () {
var i, index;
var frame;
var n = 1;
var pages = app.documents[0].pages.everyItem().getElements();
for (i = pages.length-1; i >= 0; i--) {
n--;
if (pages[i].textFrames.item('folio').isValid) {
pages[i].textFrames.item('folio').remove();
}
if (pages[i].appliedMaster !== null) {
index = pages[i].side === PageSideOptions.LEFT_HAND ? 0 : 1;
frame = pages[i].appliedMaster.pages[index].textFrames.item('folio');
if (frame.isValid) {
frame = frame.duplicate (pages[i]);
frame.contents = String(n);
}
}
}
}());
When you add and/or delete pages, simply run the script again.
Peter