look here(i don't follow this thred so i cant say that it is working now, or not): http://www.opserver.de/ubb7/ubbthreads.php?ubb=showflat&Number=355335#Post355335
maybe you can "copy" your old mesh an add the new to it, u have just merge the vertices(so that you havn't two vertices at one point) and remove the sensless polys. i cant give you an example, sorry. and i don't know how fast it is.
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Es ist immer wieder erstaunlich, dass Leute die riesen Scripte schreiben die einfachsten sachen nicht können zb. mich mit SIEBEN x zu schreiben! tongue