Is there anyway to import new icons to a copy of another fontpack?

[wert...@gmail.com]

We are using the Icomoon Ultimate fontpack along with several of our own icons.

Our version of the Ultimate pack is however quite a bit old and now we want to include all the new icons in our custom pack whilst keeping all the existing icon names, so we don't need to change all our classes in our code.

I can copy all the icons from the Ultimate set to our custom set but that ends up with several duplicates.

If I start a new set from the Ultimate set and copy our custom icons into this many of our icons look wrong because the arrow-left2 is now arrow-left4 etc.

Any suggestions?